Three dimensional printing

ABSTRACT

Various embodiments related to three dimensional printers, and reinforced filaments, and their methods of use are described. In one embodiment, a void free reinforced filament is fed into an extrusion nozzle. The reinforced filament includes a core, which may be continuous or semi-continuous, and a matrix material surrounding the core. The reinforced filament is heated to a temperature greater than a melting temperature of the matrix material and less than a melting temperature of the core prior to extruding the filament from the extrusion nozzle.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/134,451, filed Sep. 18, 2018, which is a continuation of U.S. patentapplication Ser. No. 15/206,569, filed Jul. 11, 2016 [now U.S. Pat. No.10,076,876], which is a continuation of U.S. patent application Ser. No.15/179,223, filed Jun. 10, 2016 [Abandoned], the disclosure of which isherein incorporated by reference in its entirety. The Ser. No.15/179,223 application is a continuation of U.S. patent application Ser.No. 14/222,318, filed Mar. 21, 2014 [Abandoned], the disclosure of whichis herein incorporated by reference in its entirety. The Ser. No.14/222,318 application claims the benefit under 35 U.S.C. § 119(e) ofU.S. provisional application Ser. No. 61/804,235, filed Mar. 22, 2013[Expired], U.S. provisional application Ser. No. 61/815,531, filed Apr.24, 2013 [Expired], U.S. provisional application Ser. No. 61/831,600,filed Jun. 5, 2013 [Expired], U.S. provisional application Ser. No.61/847,113, filed Jul. 17, 2013 [Expired], U.S. provisional applicationSer. No. 61/878,029, filed Sep. 15, 2013 [Expired], U.S. provisionalapplication Ser. No. 61/880,129, filed Sep. 19, 2013 [Expired], U.S.provisional application Ser. No. 61/881,946, filed Sep. 24, 2013[Expired], U.S. provisional application Ser. No. 61/883,440, filed Sep.27, 2013 [Expired], U.S. provisional application Ser. No. 61/902,256,filed Nov. 10, 2013 [Expired], and U.S. provisional application Ser. No.61/907,431, filed Nov. 22, 2013 [Expired], the disclosures of which areincorporated by reference in their entirety.

FIELD

Aspects relate to three dimensional printing.

BACKGROUND

Since the initial development of three dimensional printing, also knownas additive manufacturing, various types of three dimensional printingand printers for building a part layer by layer have been conceived. Forexample, Stereolithography (SLA) produces high-resolution parts.However, parts produced using SLA typically are not durable and are alsooften not UV-stable and instead are typically used for proof-of-conceptwork. In addition to SLA, Fused Filament Fabrication (FFF) threedimensional printers are also used to build parts by depositingsuccessive filament beads of acrylonitrile butadiene styrene (ABS), or asimilar polymer. In a somewhat similar technique, “towpregs” includingcontinuous fiber reinforced materials including a resin are deposited ina “green state”. Subsequently, the part is placed under vacuum andheated to remove entrapped air voids present in the deposited materialsand fully cure the part. Another method of additive manufacturing,though not considered three-dimensional printing, includespreimpregnated (prepreg) composite construction where a part is made bycutting sheets of fabric impregnated with a resin binder intotwo-dimensional patterns. One or more of the individual sheets are thenlayered into a mold and heated to liquefy the binding resin and cure thefinal part. Yet another method of (non-three-dimensional printing)composite construction is filament winding which uses strands ofcomposite (containing hundreds to thousands of individual carbon strandsfor example) that are wound around a custom mandrel to form a part.Filament winding is typically limited to concave shapes due to thefilaments “bridging” any convex shape due to the fibers being undertension and the surrounding higher geometry supporting the fibers sothat they do not fall into the underlying space.

SUMMARY

In one embodiment, a method for manufacturing a part includes: feeding avoid free core reinforced filament into an extrusion nozzle, wherein thecore reinforced filament comprises a core and a matrix materialsurrounding the core; heating the core reinforced filament to atemperature greater than a melting temperature of the matrix materialand less than a melting temperature of the core; and extruding the corereinforced filament to form the part.

In another embodiment, a filament for use with a three dimensionalprinter includes a multifilament core and a matrix material surroundingthe multifilament core. The matrix material is substantially impregnatedinto the entire cross-section of the multifilament core, and thefilament is substantially void free.

In yet another embodiment, a method for manufacturing a part, the methodincludes: feeding a filament into a heated extrusion nozzle; and cuttingthe filament at a location at or upstream from an outlet of the heatednozzle.

In another embodiment, a three dimensional printer includes a heatedextrusion nozzle including a nozzle outlet and a feeding mechanismconstructed and arranged to feed a filament into the heated extrusionnozzle. The three dimensional printer also includes a cutting mechanismconstructed and arranged to cut the filament at a location at, orupstream from, the heated nozzle outlet.

In yet another embodiment, a heated extrusion nozzle includes a nozzleinlet constructed and arranged to accept a filament and a nozzle outletin fluid communication with the nozzle inlet. A cross-sectional area ofthe nozzle outlet transverse to a path of the filament is larger than across-sectional area of the nozzle inlet transverse to the path of thefilament.

In another embodiment, a filament for use with a three dimensionalprinter includes a core including a plurality of separate segmentsextending in an axial direction of the filament and a matrix materialsurrounding the plurality of segments. The matrix material issubstantially impregnated into the entire cross-section of the core, andthe filament is substantially voidfree.

In yet another embodiment, a method includes: positioning a filament ata location upstream of a nozzle outlet where a temperature of the nozzleis below the melting temperature of the filament; and displacing thefilament out of the nozzle outlet during a printing process.

In another embodiment, a method includes: feeding a filament from afirst channel sized and arranged to support the filament to a cavity influid communication a nozzle outlet, wherein a cross-sectional area ofthe cavity transverse to a path of the filament is larger than across-sectional area of the first channel transverse to the path of thefilament.

In yet another embodiment, a method for forming a filament includes:mixing one or more fibers with a first matrix material to form a corereinforced filament; and passing the filament through a circuitous pathto impregnate the first matrix material into the one or more fibers.

In another embodiment, a method includes: coextruding a core reinforcedfilament and a coating matrix material to form an outer coating on thecore reinforced filament with the coating material.

In yet another embodiment, a method for manufacturing a part includes:feeding a filament into a heated extrusion nozzle; extruding thefilament from a nozzle outlet; and

applying a compressive force to the extruded filament with the nozzle.

In another embodiment, a method for manufacturing a part includes:depositing a first filament into a layer of matrix material in a firstdesired pattern using a printer head; and curing at least a portion ofthe matrix layer to form a layer of a part including the deposited firstfilament.

It should be appreciated that the foregoing concepts, and additionalconcepts discussed below, may be arranged in any suitable combination,as the present disclosure is not limited in this respect. Further, otheradvantages and novel features of the present disclosure will becomeapparent from the following detailed description of various non-limitingembodiments when considered in conjunction with the accompanyingfigures.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings are not intended to be drawn to scale. In thedrawings, each identical or nearly identical component that isillustrated in various figures may be represented by a like numeral. Forpurposes of clarity, not every component may be labeled in everydrawing. In the drawings:

FIG. 1 is a schematic representation of a three dimensional printingsystem using a continuous core reinforced filament:

FIG. 2 is a representative flow chart of a three dimensional printingprocess;

FIG. 3A is a schematic representation of a continuous core reinforcedfilament including a solid continuous core and surrounding thermoplasticresin with a smaller proportion of solid continuous core:

FIG. 3B is a schematic representation of a continuous core reinforcedfilament including a solid continuous core surrounded by thermoplasticresin with a larger proportion of solid continuous core:

FIG. 3C is a schematic representation of a continuous core reinforcedfilament including a multifilament continuous core surrounded bythermoplastic resin with a smaller proportion of the multifilamentcontinuous core;

FIG. 3D is a schematic representation of a continuous core reinforcedfilament including a multifilament continuous core surrounded bythermoplastic resin with a large proportion of the multifilamentcontinuous core;

FIG. 3E is a schematic representation of a continuous core reinforcedfilament including a multifilament continuous core including elementswith electrical, optical, or fluidic properties;

FIG. 4 is a schematic representation of a prior art nozzle and a towpregincluding voids;

FIG. 5 is a schematic representation of fiber bunching within a priorart nozzle;

FIG. 6A is a schematic representation of a divergent nozzle utilized insome embodiments of the printing system;

FIG. 6B is a schematic representation of a straight nozzle utilized insome embodiments of the printing system;

FIG. 6C is a schematic representation of a rounded tip nozzle utilizedin some embodiments of the printing system:

FIG. 7 is a schematic representation of a prior art three dimensionalprinting system:

FIG. 8 is a schematic representation of a three dimensional printingsystem including a cutting mechanism and a printing process bridging anopen space;

FIG. 9 is a schematic representation of a part formed by thethree-dimensional printing system and/or process that includes anenclosed open space;

FIG. 10 is a schematic representation of a three-dimensional printingsystem including a guide tube;

FIG. 11 is a photograph of a three dimensional printing system includinga guide tube:

FIG. 12A is a schematic representation of a shear cutting head withoptional indexing positions:

FIG. 12B is a schematic representation of the shear cutting head of FIG.11A in a second indexing position:

FIG. 13 is a schematic representation of a multi-nozzle print headincluding shear cutting:

FIG. 14A is a schematic representation of a nozzle;

FIG. 14B is a schematic representation of a nozzle having a roundedoutlet;

FIG. 14C is a schematic representation of another nozzle having arounded outlet:

FIG. 15A is a schematic cross-sectional view of a cutting mechanismintegrated with a nozzle tip;

FIG. 15B is a schematic cross-sectional view of the cutting mechanismintegrated with a nozzle tip depicted in FIG. 14A rotated 90°;

FIG. 15C is a bottom view of one embodiment of a cutting mechanismintegrated with a nozzle tip;

FIG. 15D is a bottom view of one embodiment of a cutting mechanismintegrated with a nozzle tip;

FIG. 16 is a schematic cross-sectional view of a cutting mechanismintegrated with a nozzle tip;

FIG. 17A is a schematic representation of a three-dimensional printingsystem applying a compaction pressure during part formation;

FIG. 17B is a schematic representation of a continuous core reinforcedfilament to be utilized with the printing system prior to deposition;

FIG. 17C is a schematic representation of the continuous core reinforcedfilament and surrounding beads of materials after deposition usingcompaction pressure;

FIG. 18A is a schematic representation of a prior art nozzle:

FIG. 18B is a schematic representation of a divergent nozzle;

FIG. 18C is a schematic representation of the divergent nozzle of FIG.18B shown in a feed forward cleaning cycle:

FIG. 19A is a schematic representation of a continuous core filamentbeing printed with a straight nozzle;

FIG. 19B is a schematic representation of a green towpreg being printedwith a straight nozzle;

FIGS. 19C-19E are schematic representations of a continuous corefilament being stitched and printed with a divergent nozzle;

FIG. 20A is a schematic representation of a multi-material nozzle with alow friction cold feeding zone;

FIG. 20B is a schematic representation of a slightly convergent nozzleincluding a low friction cold feeding zone:

FIG. 21A is a schematic representation of a prior art nozzle;

FIGS. 21B-21D represent various embodiments of nozzle geometries;

FIG. 22 is a schematic representation of an anti-drip nozzle andpressure reduction system;

FIG. 23A is a schematic representation of a semi-continuous corefilament positioned within a nozzle:

FIG. 23B is a schematic representation of a semi-continuous corefilament with overlapping strands positioned within a nozzle:

FIG. 23C is a schematic representation of a semi-continuous corefilament with aligned strands and positioned within a nozzle:

FIG. 24A is a schematic representation of a multifilament continuouscore:

FIG. 24B is a schematic representation of a semi-continuous corefilament with offset strands:

FIG. 24C is a schematic representation of a semi-continuous corefilament with aligned strands:

FIG. 24D is a schematic representation of a semi-continuous corefilament with aligned strands and one or more continuous strands:

FIG. 25 is a schematic representation of a fill pattern using asemi-continuous core filament;

FIG. 26 is a schematic representation of multiple printed layers formedby the three-dimensional printing system and/or process with thedifferent layers and different portions of the layers includingdifferent fiber directions;

FIG. 27A is a schematic representation of a three dimensional printingprocess for forming a component in a first orientation;

FIG. 27B is a schematic representation of a fixture to use with the partof FIG. 27A:

FIG. 27C is a schematic representation of a three dimensional printingprocess for forming a component on the part of FIG. 27A in a secondorientation;

FIG. 28A is a schematic representation of a three dimensional printingprocess using a multiaxis system in a first orientation;

FIG. 28B is a schematic representation of forming a component in anotherorientation on the part of FIG. 28A:

FIG. 29 is a schematic representation of a three dimensional printingsystem using a continuous core reinforced filament:

FIG. 30A is a schematic representation of a part including a shellapplied to the sides using a three dimensional printing process;

FIG. 30B is a schematic representation of a part including a shellapplied to the top and sides using a three-dimensional printing process;

FIG. 30C is a schematic representation of a part including a shell thathas been offset from an underlying supporting surface:

FIG. 30D is a schematic representation of a part formed with a fillmaterial:

FIG. 30E is a schematic representation of a part formed with compositematerial extending inwards from the corners and polymer fill in theinterior;

FIG. 30F is a schematic representation of a part formed with compositematerial extending inwards from the corners and polymer fill in theinterior;

FIG. 30G is a schematic representation of a part formed with compositematerial extending inwards from the corners and polymer fill in theinterior:

FIG. 31A is a schematic representation of an airfoil formed withdiscrete subsections including fiber orientations in the same direction:

FIG. 31B is a schematic representation of an airfoil formed withdiscrete subsections including fiber orientations in differentdirections;

FIG. 31C is a schematic representation of an airfoil formed withdiscrete subsections and a shell formed thereon:

FIG. 32 is a schematic representation of a three dimensional printingsystem including a print arm and selectable printer heads;

FIG. 33 is a schematic representation of a multi-element printer headfor use in the printing system;

FIG. 34 is a schematic representation of a stereolithography threedimensional printing process including deposited reinforcing fibers:

FIG. 35 is a schematic representation of a stereolithography threedimensional printing process including deposited reinforcing fibers;

FIG. 36 is a schematic representation of a three dimensional printedpart including incorporated printed components with differentfunctionalities;

FIG. 37 is a schematic representation of a three dimensional printingsystem being used to form multiple layers in a printed circuit board;

FIG. 38 is a schematic representation of a three dimensional printingsystem being used to fill various voids in a printed circuit board withsolder or solder paste;

FIG. 39 is a schematic representation of the print circuit board of FIG.38 after the formation of vias and contact pads:

FIG. 40A is a schematic representation of a printed part including ahole drilled therein;

FIG. 40B is a schematic representation of a printed part including areinforced hole formed therein:

FIG. 40C is a schematic representation of a printed part including areinforced hole formed therein;

FIG. 41A is a schematic representation of a composite part formed usingthree-dimensional printing methods; and

FIG. 41B is a scanning electron microscope image of a reinforcing carbonfiber and perpendicularly arranged carbon nanotubes;

FIG. 42 is a schematic representation of a circuitous path impregnationsystem

FIG. 43A is a schematic representation of an incoming material withcomingled tows;

FIG. 43B is a schematic representation of the material of FIG. 43A afterimpregnation;

FIG. 44A is a schematic representation of an offset roller impregnationsystem;

FIG. 44B is a schematic representation of the roller impregnation systemof FIG. 44A in an optional loading configuration:

FIG. 45 is a schematic representation of an impregnation system combinedwith a vacuum impregnation nozzle;

FIG. 46 is a schematic representation of an impregnation systemintegrated with a printing nozzle;

FIG. 47 is a schematic representation of a printing nozzle including acircuitous path impregnation system:

FIG. 48 is a schematic representation of a multi-nozzlethree-dimensional printer:

FIG. 49A is a schematic representation of a co-extrusion process to forma continuous core reinforced filament and an optional outer coating:

FIG. 49B is a schematic representation of a starting material used inthe process depicted in FIG. 49A:

FIG. 49C is a schematic representation of a starting material used inthe process depicted in FIG. 49A;

FIG. 49D is a schematic representation of one embodiment of a materialafter impregnation using the process depicted in FIG. 49A;

FIG. 49E is a schematic representation of one embodiment of a materialafter impregnation using the process depicted in FIG. 49A;

FIG. 49F is a schematic representation of one embodiment of a materialafter impregnation using the process depicted in FIG. 49A:

FIG. 49G is a schematic representation of one embodiment of a materialincluding an optional outer coating using the process depicted in 49A:

FIG. 49H is a schematic representation of one embodiment of a materialincluding an optional outer coating using the process depicted in 49A:

FIG. 49I is a schematic representation of one embodiment of a materialincluding an optional outer coating using the process depicted in 49A:

FIG. 50A is a schematic representation of a co-extrusion process to forma continuous core reinforced filament and an optional outer coating;

FIG. 50B is a schematic representation of a starting material used inthe process depicted in FIG. 50A:

FIG. 50C is a schematic representation of a starting material used inthe process depicted in FIG. 49A;

FIG. 50D is a schematic representation of a starting material afterbeing spread out using the process depicted in FIG. 50A:

FIG. 50E is a schematic representation of one embodiment of a materialafter impregnation using the process depicted in FIG. 50A;

FIG. 50F is a schematic representation of one embodiment of a materialafter shaping using the process depicted in FIG. 50A:

FIG. 50G is a schematic representation of one embodiment of a materialafter shaping using the process depicted in FIG. 50A:

FIG. 50H is a schematic representation of one embodiment of a materialafter shaping using the process depicted in FIG. 50A; and

FIG. 50I is a schematic representation of one embodiment of a materialincluding an optional outer coating using the process depicted in 50A.

DETAILED DESCRIPTION

The inventors have recognized that one of the fundamental limitationsassociated with typical additive manufacturing methods is the strengthand durability of the resulting part. For example, Fused FilamentFabrication results in a part exhibiting a lower strength than acomparable injection molded part. Without wishing to be bound by theory,this reduction in strength is due to weaker bonding between theadjoining strips of deposited material (as well as air pockets andvoids) as compared to the continuous and substantially void freematerial formed, for example, during injection molding. The inventorshave also recognized that the prepreg composite construction methodsusing a sheet-based approach to form a three dimensional part are bothtime consuming and difficult to handle resulting in higher expenses.Further, bending such sheets around curves, a circle for example, maycause the fibers to overlap, buckle, and/or distort resulting inundesirable soft spots in the resultant component. With regards to threedimensional printers using “towpregs” or “tows” including reinforcingfibers and a resin, the inventors have noted that the prior artdeposited materials are often difficult to load in the machine, andfurther difficult to feed through the print head, due to their extremelyflexible, and usually high-friction (sticky) initial state. Further,these green materials tend to entrap air and include air voids. Thus,without a subsequent vacuum and heating step, the resultant part alsocontains voids, and is substantially weaker than a traditional compositepart constructed under a vacuum. Therefore, the additional stepsassociated with preparing a towpreg slow down the printing process andresult in the entrapment of ambient air.

Due to the limitations associated with typical three dimensionalprinting systems noted above, the inventors have recognized a need toimprove the strength of three dimensional printed composites. Further,there is a need for additive manufacturing construction techniques thatallow for greater speed; removal or prevention of entrapped air in thedeposited material: reduction of the need for subsequent vacuumingsteps; and/or correct and accurate extrusion of the composite corematerial. The inventors have also recognized that it is desirable toprovide the ability to deposit fibers in concave shapes, and/orconstruct discrete features on a surface or composite shell.

In view of the above, the inventors have recognized the benefitsassociated with providing a three dimensional printing system thatprints structures using a substantially void-free preimpregnated(prepreg) material, or that is capable of forming a substantially voidfree material for use in the deposition process. For example, in oneembodiment, a three dimensional printer uses a continuous corereinforced filament including a continuous multifilament core materialwith multiple continuous strands that are preimpregnated with athermoplastic resin that has already been “wicked” into the strands,such a preimpregnated material is then used to form a three dimensionalstructure. Due to the thermoplastic resin having already wicked into thestrands, the material is not “green” and is also rigid, low-friction,and substantially void free. In another embodiment, a solid continuouscore is used and the thermoplastic resin wets the solid continuous coresuch that the resulting continuous core reinforced filament is alsosubstantially void free. Additionally, embodiments in which asemi-continuous core is used in which a core extending through thelength of a material is sectioned into a plurality of portions along thelength is also contemplated. Such an embodiment may include either asolid core or multiple individual strands that are either evenly spacedfrom one another or include overlaps as the disclosure is not solimited. In either case, such a core material may also be preimpregnatedor wetted as noted above. A substantially void free material may have avoid percentage that is less than about 1%, 2%, 3%, 4%, 5%, 10%, 13%, orany other appropriate percentage. For example, the void free materialmay have a void percentage that is between about 1% and 5%.Additionally, due to the processing methods described below, partsprinted using the above-noted void free material may also exhibit voidpercentages less than about 1%, 2%, 3%, 4%, 5%, 10%, or 13%.

While preimpregnated materials are discussed above, in one embodiment, asolid continuous core filament may be selectively combined with a resinin a nozzle outlet. Without wishing to be bound by theory, due to theregular and well-defined geometry of the solid core, the resin evenlycoats the core and the resulting deposited composite material issubstantially free from voids.

Within this application, core reinforced filaments are described asbeing either impregnated or wetted. For example, a solid core might belet with a matrix material, or a multifilament core may be bothimpregnated and fully wet with a matrix material. However, for thepurposes of this application, a filament including a core that has beenimpregnated should be understood to refer to a filament including a corethat has been fully impregnated and/or wet with matrix material. Aperson of ordinary skill would be able to understand how this might beinterpreted for applications where a core material is a solid core.

In addition to the above, a core reinforced material as describedthroughout this application. For specific embodiments and examples, acontinuous core and/or a semi-continuous core might be described forexemplary purposes. However, it should be understood that either acontinuous and/or a semi-continuous core might be used in any particularapplication and the disclosure is not limited in this fashion.Additionally, with regards to a core reinforced material, the core mayeither be positioned within an interior of the filament or the corematerial may extend to an exterior surface of the filament as thedisclosure is not limited in this fashion. Additionally, it should beunderstood that a court reinforced material also includes reinforcementsprovided by materials such as optical materials, fluid conductingmaterials, electrically conductive materials as well as any otherappropriate material as the disclosure is not so limited.

In yet another embodiment, the inventors have recognized the benefitsassociated with providing a continuous or semi-continuous core combinedwith stereolithography (SLA), selective laser sintering (SLS), and otherthree dimensional printing processes using a matrix in liquid or powderform to form a substantially void free parts exhibiting enhancedstrength. The above embodiments may help to reduce, or eliminate, theneed for a subsequent vacuum step as well as improve the strength of theresulting printed structures by helping to reduce or eliminate thepresence of voids within the final structure.

In addition to improvements in strength due to the elimination of voids,the inventors have recognized that the current limitation of laying downa single strip at a time in three dimensional printing processes may beused as an advantage in composite structure manufacturing. For example,the direction of reinforcing materials deposited during the printingprocess within a structure may be controlled within specific layers andportions of layers to control the directional strength of the compositestructure both locally and overall. Consequently, the directionality ofreinforcement within a structure can provide enhanced part strength indesired locations and directions to meet specific design requirements.The ability to easily tailor the directional strength of the structurein specific locations may enable both lighter and stronger resultingparts.

In embodiments, it may be desirable to include a cutting mechanism withthe three dimensional printing system. Such a cutting mechanism may beused to provide selective termination in order to deposit a desiredlength of material. Otherwise, the printing process could not be easilyterminated due to the deposited material still being connected to thematerial within the extrusion nozzle b, for example, a continuous core.The cutting mechanism may be located at the outlet of the associatedprinter nozzle or may be located upstream from the outlet. Further, insome embodiments, the cutting mechanism is located between a feedingmechanism for the core material and the outlet of the nozzle. Howeverregardless of the specific configuration and location, the cuttingmechanism enables the three dimensional printing system to quickly andeasily deposit a desired length of material in a desired direction at aparticular location. In contrast, systems which do not include a cuttingmechanism continuously deposit material until the material runs out orit is manually cut. This limits both the complexity of the parts thatcan be produced, the speed of the printing process as well as theability to deposit the material including the continuous core in aparticular direction. Depending on the embodiment, the cutting mechanismmay also interrupt the printer feed by blocking the nozzle or preventingthe feeding mechanism from applying force or pressure to a portion ofthe material downstream from the cutting mechanism. While in some casesit may be desirable to include a cutting mechanism with the threedimensional printer, it should be understood that embodiments describedherein may be used both with and without a cutting mechanism as thecurrent disclosure is not limited in this fashion. Further, a cuttingmechanism may also be used with embodiments that do not include acontinuous core.

It should be understood that the substantially void free materialdescribed herein may be manufactured in any number of ways. However, inone embodiment, the material is formed by applying a varying pressureand/or forces in different directions during formation of the material.For example, in one embodiment, multiple strands of a polymer or resinand a core including a plurality of reinforcing fibers are co-mingledprior to feeding into a system. The system then heats the materials to adesired viscosity of the polymer resin and applies varying pressuresand/or forces in alternating directions to the comingled towpreg to helpfacilitate fully impregnating the fibers of the towpreg with the polymeror resin. This may be accomplished using a smooth circuitous pathincluding multiple bends through which a green towpreg is passed, or itmay correspond to multiple offset rollers that change a direction of thetowpreg as it is passed through the system. As the towpreg passesthrough this circuitous path, the varying forces and pressures help tofully impregnate the polymer into the core and form a substantially voidfree material. While a co-mingled towpreg including separate strands ofreinforcing fibers and polymer resin are described above, embodiments inwhich a solid core and/or multiple reinforcing fibers are comingled withpolymer particles, or dipped into a liquid polymer or resin, and thensubjected to the above noted process are also contemplated. In additionto the above, after impregnating the core with the polymer, thesubstantially void free material may be fed through a shaping nozzle toprovide a desired shape. The nozzle may be any appropriate shapeincluding a circle, an oval, a square, or any other desired shape. Whilea continuous core is noted above, embodiments in which a semi-continuouscore is used are also contemplated. Additionally, this formation processmay either be performed under ambient conditions, or under a vacuum tofurther eliminate the presence of voids within the substantially voidfree material.

In some embodiments, it may be desirable to provide a smooth outercoating on a towpreg corresponding to the substantially void freematerial noted above. In such an embodiment, a substantially void freematerial, which is formed as noted above, or in any other appropriateprocess, is co-extruded with a polymer through an appropriately shapednozzle. As the substantially void free material and polymer are extrudedthrough the nozzle, the polymer forms a smooth outer coating around thesubstantially void free material.

The materials used with the currently described three dimensionalprinting processes may incorporate any appropriate combination ofmaterials. For example appropriate resins and polymers include, but arenot limited to, acrylonitrile butadiene styrene (ABS), epoxy, vinyl,nylon, polyetherimide (PEI), Polyether ether ketone (PEEK), PolylacticAcid (PLA), Liquid Crystal Polymer, and various other thermoplastics.The core may also be selected to provide any desired property.Appropriate core filaments include those materials which impart adesired property, such as structural, conductive (electrically and/orthermally), insulative (electrically and/or thermally), optical and/orfluidic transport. Such materials include, but are not limited to,carbon fibers, aramid fibers, fiberglass, metals (such as copper,silver, gold, tin, steel), optical fibers, and flexible tubes. It shouldbe understood that the core filaments may be provided in any appropriatesize. Further, multiple types of continuous cores may be used in asingle continuous core reinforced filament to provide multiplefunctionalities such as both electrical and optical properties. Itshould also be understood that a single material may be used to providemultiple properties for the core reinforced filament. For example, asteel core might be used to provide both structural properties as wellas electrical conductivity properties.

In some embodiments, in addition to selecting the materials of the corereinforced filament, it is desirable to provide the ability to use corereinforced filaments with different resin to reinforcing core ratios toprovide different properties within different sections of the part. Forexample, a low-resin filler may be used for the internal construction ofa part, to maximize the strength-to-weight ratio (20% resin by crosssectional area, for example). However, on the outer cosmetic surface ofthe part, a higher, 90% resin consumable may be used to prevent thepossible print through of an underlying core or individual fiber strandof the core. Additionally, in some embodiments, the consumable materialmay have zero fiber content, and be exclusively resin. Therefore, itshould be understood that any appropriate percentage of resin may beused.

The core reinforced filaments may also be provided in a variety ofsizes. For example, a continuous or semi-continuous core reinforcedfilament may have an outer diameter that is greater than or equal toabout 0.001 inches and less than or equal to about 0.4 inches. In onespecific embodiment, the filament is greater than or equal to about0.010 inches and less than or equal to about 0.030 inches. In someembodiments, it is also desirable that the core reinforced filamentincludes a substantially constant outer diameter along its length.Depending on the particular embodiment, different smoothnesses andtolerances with regards to the core reinforced filament outer diametermay be used. Without wishing to be bound by theory, a constant outerdiameter may help to provide constant material flow rate and uniformproperties in the final part.

As described in more detail below, the ability to selectively printelectrically conductive, optically conductive, and/or fluidly conductivecores within a structure enables the construction of desired componentsin the structure. For example, electrically conductive and opticallyconductive continuous cores may be used to construct strain gauges,optical sensors, traces, antennas, wiring, and other appropriatecomponents. Fluid conducting cores might also be used for formingcomponents such as fluid channels and heat exchangers. The ability toform functional components on, or in, a structure offers multiplebenefits. For example, the described three dimensional printingprocesses and apparatuses may be used to manufacture printed circuitboards integrally formed in a structure; integrally formed wiring andsensors in a car chassis or plane fuselage; as well as motor cores withintegrally formed windings to name a few.

Turning now to the figures, specific embodiments of the disclosedmaterials and three dimensional printing processes are described.

FIG. 1 depicts an embodiment of a three dimensional printer usingcontinuous strands of composite material to build a structure. In thedepicted embodiment, the continuous strand of composite material is acontinuous core reinforced filament 2. The continuous core reinforcedfilament 2 is a towpreg that is substantially void free and includes apolymer 4 that coats or impregnates an internal continuous core 6.Depending upon the particular embodiment, the core 6 may be a solid coreor it may be a multifilament core including multiple strands.

The continuous core reinforced filament 2 is fed through a heatednozzle, such as extrusion nozzle 10. As the continuous core reinforcedfilament is fed through the extrusion nozzle it is heated to apreselected extrusion temperature. This temperature may be selected toeffect any number of resulting properties including, but not limited to,viscosity of the extruded material, bonding of the extruded material tothe underlying layers, and the resulting surface finish. While theextrusion temperature may be any appropriate temperature, in oneembodiment, the extrusion temperature is greater than the meltingtemperature of the polymer 4, but is less than the decompositiontemperature of the resin and the melting or decomposition temperature ofthe core 6. Any suitable heater may be employed to heat the nozzle, suchas a band heater or coil heater.

After being heated in the heated extrusion nozzle 10, the continuouscore reinforced filament 2 is extruded onto a build platen 16 to buildsuccessive layers 14 to form a final three dimensional structure. Theposition of the heated extrusion nozzle 10 relative to the build platen16 during the deposition process may be controlled in any appropriatefashion. For example, the position and orientation of the build platen16 or the position and orientation of the heated extrusion nozzle 10 maybe controlled by a controller 20 to deposit the continuous corereinforced filament 2 in the desired location and direction as thecurrent disclosure is not limited to any particular control method.Also, any appropriate movement mechanism may be used to control eitherthe nozzle or the build platen including gantry systems, robotic arms, Hframes, and other appropriate movement systems. The system may alsoinclude any appropriate position and displacement sensors to monitor theposition and movement of the heated extrusion nozzle relative to thebuild platen and/or a part being constructed. These sensors may thencommunicate the sensed position and movement information to thecontroller 20. The controller 20 may use the sensed X, Y, and/or Zpositions and movement information to control subsequent movements ofthe heated extrusion head or platen. For example, the system mightinclude rangefinders, displacement transducers, distance integrators,accelerometers, and/or any other sensing systems capable of detecting aposition or movement of the heated extrusion nozzle relative to thebuild platen. In one particular embodiment, and as depicted in thefigure, a laser range finder 15, or other appropriate sensor, is used toscan the section ahead of the heated extrusion nozzle in order tocorrect the Z height of the nozzle, or fill volume required, to match adesired deposition profile. This measurement may also be used to fill invoids detected in the part. Additionally, the range finder 15, oranother range finder could be used to measure the part after thematerial is extruded to confirm the depth and position of the depositedmaterial.

Depending on the embodiment, the three dimensional printer includes acutting mechanism 8. The cutting mechanism 8 advantageously permits thecontinuous core reinforced filament to be automatically cut during theprinting process without the need for manual cutting or the formation oftails as described in more detail below. By cutting the continuous corereinforced filament during the deposition process, it is possible toform separate features and components on the structure as well ascontrol the directionality of the deposited material in multiplesections and layers which results in multiple benefits as described inmore detail below. In the depicted embodiment, the cutting mechanism 8is a cutting blade associated with a backing plate 12 located at thenozzle outlet, though other locations are possible. While one embodimentof the cutting mechanism including a cutting blade is shown, other typesof cutting mechanisms as described in more detail below are alsopossible, including, but not limited to, lasers, high-pressure air,high-pressure fluid, shearing mechanisms, or any other appropriatecutting mechanism. Further, the specific cutting mechanism may beappropriately selected for the specific feed material used in the threedimensional printer.

FIG. 1 also depicts a plurality of optional secondary print heads 18that are employed with the three dimensional printer in someembodiments. A secondary print head 18 may be used to deposit inks, orother appropriate optional coatings, on the surface of a threedimensional printed part. In one embodiment, the secondary print head issimilar to an existing inkjet printer. Such a print head may be used toprint photo-quality pictures and images on the part during themanufacturing process. The print head might use UV resistant resins forsuch a printing process. Alternatively, the print head may be used toprint protective coatings on the part. For example, the print head mightbe used to provide a UV resistant or a scratch resistant coating.

FIG. 2 presents a schematic flow diagram of a three dimensional printingprocess using the system and controller depicted in FIG. 1. Initially acontinuous core reinforced filament is provided at 102. The continuouscore reinforced filament is then fed into the heated extrusion nozzleand heated to a desired temperature that is greater than a meltingtemperature of the resin and is less than a melting temperature of thecontinuous core at 104 and 106. The three dimensional printer thensenses a position and movement of the heated extrusion nozzle relativeto the build platen or part at 108. After determining the position andmovement of the heated extrusion nozzle, the nozzle is moved to adesired location and the continuous core reinforced filament is extrudedat the desired location and along a desired path and direction at 110.Embodiments are also envisioned in which the build platen or part aremoved relative to the nozzle. After reaching the desired terminationpoint, the continuous core reinforced filament is cut at 112. Thecontroller may then determine if the three dimensional part iscompleted. If the printing process is not completed the controller mayreturn to 108 during which it senses the current position and movementof the nozzle prior to depositing the next piece of continuous corereinforced filament. If the part is completed, the final part may beremoved from the build platen. Alternatively, an optional coating may bedeposited on the part using a secondary print head at 116 to provide aprotective coating and/or apply a figure or image to the final part. Itshould be understood that the above noted steps may be performed in adifferent order than presented above. Further, in some embodiments,additional steps may be used and/or omitted as the current disclosure isnot limited to only the processes depicted in FIG. 2.

FIGS. 3A-3E depict various embodiments of core configurations of acontinuous core reinforced filaments 2. In addition to the specific coreconfigurations, the materials are processed to be substantiallyvoid-free which helps with both the binding of the individual layers andresulting strength of the final structures.

FIGS. 3A and 3B depict the cross-section of a continuous core reinforcedfilament including a solid core 6 a encased in a surrounding polymer 4or resin. There are substantially no voids present either in the polymeror between the polymer and solid core. FIG. 3A depicts a continuous corereinforced filament that includes a cross section with a largerproportion of polymer. FIG. 3B depicts a cross section with a largersolid core and correspondingly larger proportion of reinforcing corematerial. It should be understood that any appropriate proportion ofcontinuous core area to polymer area may be used. Further, withoutwishing to be bound by theory, materials with a larger proportion ofpolymer may result in smoother surface finishes and better adhesionbetween the layers. Conversely, larger proportions of the continuouscore filament may be used to increase the strength to weight ratio ofthe final constructed component since the fiber material constitutes thebulk of the strength of the composite and is present in a largerproportion. A larger core may also be advantageous when the core is madefrom copper or another appropriate electrically or optically conductivematerial, since it may be desirable to have a large core to increase theconductivity of the deposited material.

FIGS. 3C and 3D depict yet another embodiment in which the core materialof the continuous core reinforced filament 2 is a continuousmultifilament core material 6 b surrounded by and impregnated with apolymer 4 which is wicked into the cross section of the multifilamentcore. FIG. 3C depicts a smaller proportion of multifilament corematerial 6 b surrounded by and impregnated with the polymer 4. FIG. 3Dillustrates an embodiment with a very small amount of resin and a largeproportion of multifilament core material 6 b such that themultifilament core material fills virtually the entire cross section. Insuch an embodiment, the polymer 4 acts more as a binder impregnated intothe multifilament core material 6 b to hold it together. Similar to theabove noted solid cores, any appropriate proportion of resin tomultifilament core material may be used to provide a selected strength,surface finish, conductivity, adhesion, or other desired property to theresulting continuous core reinforced filament 2.

FIG. 3E, depicts a variation of the continuous multifilament core. Inthis embodiment, the continuous core reinforced filament 2 stillincludes a continuous multifilament core material 6 b surrounded by andimpregnated with a polymer 4. However, the core also includes one ormore secondary strands of core materials 6 c and 6 d. These secondarycore materials might be optically conducting, electrically conducting,thermally conducting, fluid conducting, or some combination of theabove. These secondary core materials could be used to conduct power,signals, heat, and fluids as well as for structural health monitoringand other desired functionalities.

In order to avoid the entrapment of voids within the core reinforcedfilament 2 described above, the polymer material is processed such thatthe molten polymer or polymer resin wicks into the reinforcing fibersduring the initial production of the material. In some embodiments, thepolymer is substantially wicked into the entire cross-section of amultifilament core which helps to provide a substantially void freematerial. To produce the desired core reinforced filaments, the corereinforced filament may be pre-treated with one or more coatings toactivate the surface, and subsequently exposed to one or moreenvironmental conditions such as temperature, pressure, and/or chemicalagents such as plasticizers, to aid the polymer or resin wicking intothe cross section of the multifilament core without the formation of anyvoids. In some embodiments, this process may be performed prior toentering a feed head of the three dimensional printer. However, in otherembodiments, the core reinforced filament is formed on a completelyseparate machine prior to the printing process and is provided as aconsumable printing material. Since the subsequent deposition processdoes not need to be run at temperatures high enough to wet the corematerials with the polymer or resin, the deposition process can be runat lower temperatures and pressures than required in typical systems.While the above process may be applied to both the solid andmultifilament cores, it is more beneficial to apply this process to themultifilament cores due to the difficulty associated with wicking intothe multifilament core without forming voids. Further, by forming thecore reinforced filament either separately or prior to introduction tothe nozzle, the material width and proportions may be tightly controlledresulting in a more constant feed rate of material when it is fed into athree dimensional printer.

In contrast to the above materials formed substantially without voids,the prior art has employed “green” deposition processes includingreinforcing filaments that have been dipped into a resin or moltenpolymer and wicked with the multifilament cores during the extrusionprocess itself might also be use. In order to do this, the resin orpolymer is heated substantially past the melting point, such that theviscosity is sufficiently low to allow the resin or polymer to wick intothe reinforcing fibers. This process may be aided by a set of rollerswhich apply pressure to the materials to aid in wicking into thereinforcing fibers. However, due to the arrangement of the rollers andthe temperature of the temperature of the towpreg as it exits therollers, this process typically results in voids being entrapped in thematerial prior to final formation. After the resin or polymer has wickedinto the reinforcing fibers, the resulting “towpreg” or “tow” istypically cooled to just above the melting point prior to extrusion.However, this process is typically done in air which combined with theair present in the material when it is inserted into the nozzle resultsin ambient air being entrapped in the material as described in moredetail below.

Such a wicking process during the extrusion of a typical towpreg isdepicted in FIG. 4. As depicted in the figure, prior to the wicking andextrusion process, a green towpreg 22 includes multiple green matrixresin particles or filaments 24 mixed with multiple reinforcing fibers28 as well as a surrounding amount of air 24. As depicted in the figure,the reinforcing fibers 28 are distributed randomly across the crosssection. As the towpreg 22 passes through heating zone 30 of theextrusion nozzle, the material is heated to induce fiber wetting andform a cured resin 32. The surrounding air 26 also becomes entrapped inthe towpreg forming air voids 34. These entrapped air voids 34 thenbecome embedded in the resultant printed part. Additionally, the airvoids 34 may result in non-bonded sections 36 of the fibers. Since thesenon-bonded sections of the reinforcing fibers are not in contact withthe polymer, the resulting composite material will be weaker in thislocation. In contrast, the continuous core reinforced filament in theillustrative embodiment depicted in FIGS. 3A-3E are substantially freefrom voids and in at least some embodiments the cores are centrallylocated within the surrounding resin. Without wishing to be bound bytheory, this results in a stronger more uniform material and resultantpart.

While the currently described three dimensional printer systems areprimarily directed to using the preimpregnated or wetted core reinforcedfilaments described herein, in some embodiments the three dimensionalprinter system might use a material similar to the green comingledtowpreg 22 depicted in FIG. 4. However, as noted above, it is desirableto avoid the formation of entrapped air voids during curing of thematerial within the nozzle. One possible way to avoid the formation ofair voids in the deposited material, is to provide a vacuum within thenozzle. By providing a vacuum within the nozzle, there is no air toentrap within the towpreg when it is heated and cured within the nozzle.Therefore, in some embodiments, the nozzle is configured to allow theintroduction of a continuous green material including a solid ormultifilament core while under vacuum. The continuous green material maythen be heated to an appropriate temperature above the meltingtemperature of a resin or polymer within the continuous green materialwhile under vacuum to facilitate wicking of the resin or polymer intothe core to produce a substantially void free material. Another methodis the use of a circuitous path, which may be provided by offset rollersor other configurations as described below, to mechanically work out theentrapped air. Optionally, a vacuum may also be applied in conjunctionwith the mechanical removal of air bubbles through the circuitous path.

In addition to the material used for printing the three dimensionalpart, the specific nozzle used for depositing the core reinforcedfilament also has an effect on the properties of the final part. Forexample, the extrusion nozzle geometry used in typical three dimensionalprinters is a convergent nozzle, see FIG. 5. Convergent nozzles used intypical three dimensional printers typically have feed stock that isabout 0.060 inches to 0.120 inches (1.5 mm-3 mm) in diameter. This stockis squeezed through a nozzle that typically necks down to about a 0.008inch to 0.016 inch (0.2 mm-0.4 mm) tip orifice. However, such a nozzlemay not be desirable for use with feed stock including a continuous corefor the reasons described below.

Without wishing to be bound by theory, as the stock material is fed intothe converging nozzle, the constraining geometry causes the fluidpolymer matrix material to accelerate relative to the continuous core.Additionally, the matrix and core generally have different coefficientsof thermal expansion. Since the matrix material is a polymer itgenerally has a larger coefficient of thermal expansion. Therefore, asthe matrix material is heated it also accelerates relative to the fiberdue to the larger expansion of the matrix material within the confinedspace of the converging nozzle. The noted acceleration of the matrixmaterial relative to the fiber results in the matrix material flow ratev_(matrix) being less than the fiber material flow rate v_(fiber) nearthe nozzle inlet. However, the matrix material flow rate at the outletv_(matrix), is equal to the fiber material flow rate v_(fiber). Asillustrated in the figure, these mismatched velocities of the matrixmaterial and fiber within the converging nozzle may result in the fibercollecting within the nozzle during the deposition process. This maylead to clogging as well as difficulty in controlling the uniformity ofthe deposition process. It should be understood that while difficultiesassociated with a converging nozzle have been noted above, a convergingnozzle may be used with the embodiments described herein as the currentdisclosure is not limited in this fashion.

In view of the above, it is desirable to provide a nozzle geometry thatis capable of maintaining a matched velocity of the individual strandsof multifilament core material 6 b, or other appropriate core, and thepolymer 4 or other matrix material throughout the nozzle for a givenmatrix and core combination. For example, FIG. 6A depicts a divergentnozzle 200 with an increasing nozzle diameter that matches the thermalexpansion of the matrix material. As depicted in the figure, the nozzle200 includes an inlet 202 with a diameter DL, a section with anincreasing diameter 204, and an outlet 206 with a diameter D2 that isgreater than the diameter D1. Without wishing to be bound by theory, bymatching the nozzle diameter to the expected expansion of the matrixmaterial within the nozzle, the matrix and the continuous corereinforcing are kept at substantially the same velocity relative to oneanother throughout the entire nozzle. Therefore, the linear extrusionrate of the matrix material and the continuous core is the same and thecontinuous core does not build up within the nozzle.

In addition to the above, in some embodiments, the matrix material andthe continuous core have relatively low coefficients of thermalexpansion (such as carbon fiber and Liquid Crystal Polymer). In such anembodiment, since the matrix material and reinforcing fibers staysubstantially the same size, the nozzle 200 may include an inlet 202 andoutlet 206 that have substantially the same diameter D3, see FIG. 6B.Therefore, while some nozzle designs may have divergent geometries, insome embodiments the nozzle geometry may be substantially linear and mayhave substantially similar inlet and extrusion areas.

In addition to controlling the relative sizing of the nozzle inlet andoutlet, a nozzle 200 may also include a rounded nozzle outlet 208, seeFIG. 6C. The rounded nozzle outlet 208 may have any appropriate form andsize. For example, the rounded nozzle outlet 208 may be embodied by anoutwardly extending lip, a chamfer, a filet, an arc, or any otherappropriate geometry providing a smooth transition from the nozzleoutlet. Without wishing to be bound by theory, a rounded nozzle outletproviding a smooth transition from the nozzle internal bore may help toavoid applying excessive stresses to, and/or scraping, the continuousmaterial as it is extruded from the nozzle 200. This smooth transitionprovided by the rounded nozzle outlet may help to avoid fracturing thecontinuous core filament during deposition.

FIG. 7 illustrates a potential disadvantage with printing a continuouscore reinforced filament without an integrated cutter in the print head.As depicted in the figure, print head 300 is forming part 302, and isshown having deposited the last section of material layer 304. Sincetypical Fused Filament Fabrication (FFF), also known as Fused DepositionModeling (FDM), techniques place the print head close to the underlyingpart, and often touching the top of the extruded plastic, there islittle to no room in which to introduce an external cutting mechanism.Indeed, without a near zero-thickness blade, the print head needs toprint a tag-end over-run 306 not specified in the part in order toenable a separate cutting mechanism, or person, to cut the continuescore and terminate the printing process. However, this leavesundesirable tag-end over-runs 306 at each fiber termination point. Asshown in FIG. 7, a plurality of internal features, such as hard mountingbosses 308 would all have a tag-end over-run 306 at each layer withinthe boss. In view of the above, an integrated cutting mechanism mayenable less post-processing, and would allow the machine to simply printthe intended part with smaller and fewer tag-end over-runs. Further, insome embodiments, and as described in more detail below, the cuttingmechanism may eliminate the presence of tag-end over-runs altogether.

FIG. 8 depicts two embodiments of a cutting mechanism for use with athree dimensional printer. As depicted in the figure, an appropriatefeed material, which in this example is a continuous core reinforcedfilament 2 a, though other suitable filaments may be used, is removedfrom a spool 38 and passed through a feeding mechanism such as drivingroller 40 and idle wheel 42. The driving roller 40, or any otherappropriate feeding mechanism, is constructed and arranged to apply aforce directed in a downstream direction to, in this example, thecontinuous core reinforced filament 2 a. Therefore, the continuous corereinforced filament 2 a may be at a temperature such that it is in asolid or semi solid state when this force is applied. For example, theforce may be applied to the material when it is at room temperature,below a glass transition temperature of the material, between roomtemperature in the glass transition temperature, or any otherappropriate temperature at which the material is capable of supportingthe applied force. The applied downstream force results in thecontinuous core reinforced filament 2 a entering and being extruded froma heated nozzle 10 to build up a three dimensional part. While a drivingroller has been depicted, it should be understood, that any appropriatefeeding mechanism might be used.

In the first embodiment, a cutting mechanism 8 a, such as a blade, ispositioned at the outlet of the heated extrusion nozzle 10. Such aconfiguration allows actuation of the cutting mechanism to completelycut the deposited strip by severing the internal continuous core.Additionally, in some embodiments, the nozzle pressure is maintainedduring the cutting process, and the cutting blade is actuated to bothcut the internal strand, and to prevent further extrusion of thecontinuous fiber reinforced material and dripping by physically blockingthe nozzle outlet. Thus, the cutting mechanism enables the deposition ofcontinuous core reinforced filament, as well as unreinforced materials,with precisely selected lengths as compared to traditional threedimensional printers.

In the second depicted embodiment shown integrated with the same system,a cutting mechanism 8 b is located upstream from the nozzle outlet. Morespecifically, the cutting mechanism 8 b may be located within the hotend of the nozzle, or further upstream before the continuous corereinforced filament has been heated. In some embodiments, the cuttingmechanism 8 b is located between the nozzle outlet and the feedingmechanism 40. Such an embodiment may permit the use of a smaller gapbetween the nozzle outlet and the part since the cutting mechanism doesnot need to be accommodated in the space between the nozzle outlet andthe part. Depending on the particular location, the cutting mechanism 8b may cut the continuous core filament and the surrounding matrix whilethe temperature is below the melting or softening temperature and insome embodiments below the glass transition temperature. Without wishingto be bound by theory, cutting the continuous core reinforced filamentwhile it is below the melting, softening, and/or glass transitiontemperatures of the polymer may reduce the propensity of the resin tostick to the blade which may reduce machine jamming. Further, cuttingwhen the resin or polymer is below the melting point may help to enablemore precise metering of the deposited material. The position of a cutalong the continuous core reinforced filament may be selected toeliminate the presence of tag-end over-runs in the final part which mayfacilitate the formation of multiple individual features.

As shown in the figure, the downstream portion 2 b of the continuouscore reinforced filament can be severed from the upstream portion 2 a ofthe continuous core reinforced filament by the upstream cuttingmechanism 8 b. By maintaining a close fit between the feed material, andthe guiding tube within which it resides, the downstream portion 2 b ofthe cut strand can still be pushed through the machine by the upstreamportion 2 a which is driven by the drive roller 40 or any otherappropriate feeding mechanism. Without wishing to be bound by theory,the previously deposited and cooled material is also adhered to thepreviously deposited layer and will drag the continuous core reinforcedfilament 2 b out of the heated extrusion nozzle 10 when the print headis moved relative to the part which will apply a force to the continuouscore located in the downstream portion of the cut strand. Therefore, acombination of upstream forces from the feeding mechanism and downstreamforces transferred through the continuous core may be used to depositthe cut section of material. Again, the position of a cut along thecontinuous core reinforced filament may be selected to eliminate thepresence of tag-end over-runs in the final part.

While embodiments including an integrated cutting mechanism have beendepicted above, embodiments not including a cutting mechanism are alsopossible as the current disclosure is not limited in this fashion. Forexample embodiments in which a part is printed in a contiguous stringfashion, such that termination of the continuous material is notrequired might be used. In once such embodiment, the three dimensionalprinting machine might not be able to achieve fiber termination, andwould therefore print a length of material until the part was complete,the material ran out, or a user cuts the deposited material.

While cutting of the continuous fiber reinforced material helps toeliminate the presence of tag-end over-runs, it is also desirable toprevent buckling of the material to help ensure a uniform deposition andprevent machine jams. Without wishing to be bound by theory, thestiffness of a material is proportional to the diameter of the materialsquared. Therefore, continuous materials with large diameters do notneed as much support to be fed into an inlet of the nozzle as depictedin the figure. However, as the diameter of the continuous materialdecreases, additional features may be necessary to ensure that bucklingof the continuous material and any continuous core filament containedwithin it does not buckle. For example, a close-fitting guide tube asdescribed in more detail below, may be used in combination withpositioning the feeding mechanism closer to the inlet of the nozzle orguide tube to help prevent buckling of the material. Therefore, in oneembodiment, the feeding mechanism may be located within less than about20 diameters, 10 diameters, 8 diameters, 6 diameters, 5 diameters, 4diameters, 3 diameters, 2 diameters, 1 diameter, or any otherappropriate distance from a guide tube or inlet to the nozzle.

In addition to preventing buckling, in some embodiments, the maximumtension or dragging force applied to the deposited reinforcing fibers islimited to prevent the printed part from being pulled up from acorresponding build plane or to provide a desired amount of tensioningof the continuous core. The force limiting may be provided in any numberof ways. For example, a one-way locking bearing might be used to limitthe dragging force. In such an embodiment, the drive motor may rotate adrive wheel though a one-way locking bearing such that rotating themotor drives the wheel and extrudes material. If the material draggingexceeds the driven speed of the drive wheel, the one-way bearing mayslip, allowing additional material to be pulled through the feedingmechanism and nozzle, effectively increasing the feed rate to match thehead traveling speed while also limiting the driving force such that itis less than or equal to a preselected limit. The dragging force mayalso be limited using a clutch with commensurate built-in slip.Alternatively, in another embodiment, the normal force and frictioncoefficients of the drive and idler wheels may be selected to permit thecontinuous material to be pulled through the feeding mechanism above acertain dragging force. Other methods of limiting the force are alsopossible. In yet another environment, an AC induction motor, or a DCmotor switched to the “off” position (e.g. depending on the embodimentthis may correspond to either a small resistance being applied to themotor terminals or opening a motor terminals) may be used to permit thefilament to be pulled from the printer. In such an embodiment, themotors may be allowed to freewheel when a dragging force above a desiredforce threshold is applied to allow the filament to be pulled out of theprinter. In view of the above, a feeding mechanism is configured in someform or fashion such that a filament may be pulled out of the printernozzle when a dragging force applied to the filament is greater than adesired force threshold. Additionally, in some embodiments, a feedingmechanism may incorporate a sensor and controller loop to providefeedback control of either a deposition speed, printer head speed,and/or other appropriate control parameters based on the tensioning ofthe filament.

A printer system constructed to permit a filament to be pulled out of aprinter nozzle as described above, may be used in a number of ways.However, in one embodiment, the printing system drags a filament out ofa printer nozzle along straight printed sections. During such operationa printer head may be displaced at a desired rate and the depositedmaterial which is adhered to a previous layer or printing surface willapply a dragging force to the filament within the printing nozzle.Consequently, the filament will be pulled out of the printing system anddeposited onto the part. When printing along curves and/or corners, theprinting system extrudes and/or pushes the deposited filament onto apart or surface. Of course embodiments in which a filament is notdragged out of the printing system during operation and/or where afilament is dragged out of a printer head when printing a curve and/orcorner are also contemplated.

The currently described three dimensional printing methods usingcontinuous core reinforced filaments also enable the bridging of largeair gaps that previously were not able to be spanned by threedimensional printers. Without wishing to be bound by theory, thedeposition of tensioned continuous core reinforced filaments including anon-molten, i.e. solid, continuous core enables the deposited materialto be held by the print head on one end and adhesion to the printed parton the other end. The print head can then traverse an open gap, withoutthe material sagging. Thus, the printer can print in free space whichenables the printer to jump a gap, essentially printing a bridge betweentwo points. This enables the construction of hollow-core componentswithout the use of soluble support material.

FIG. 8 depicts free-space printing enabled by the continuous corereinforced filament. With the continuous core reinforced filament 2 battached to the part at point 44, and held by the print head at point46, it is possible to bridge the gap 48. In typical FFF printers, theextruded material will sag, and fall into the gap 48 because it ismolten and unsupported. However, having a continuous core of non-moltenmaterial supporting the molten polymer enables printing in free-space,advantageously enabling many new types of printing. For example, aclosed section box shown in FIG. 9 is formed by a section 50 which isbridges gap 48 and is affixed to opposing sections 52 and 54. While thisexample shows a closed section bridge, the free-space printing couldalso be used to produce cantilevers, and unsupported beams, that cannotbe printed with typical unsupported materials.

In some embodiments, a cooling mechanism such as a jet of cooling airmay be applied to the extruded material to further prevent sagging bysolidifying the polymer material surrounding the core. The extrudedmaterial may either be continuously cooled while building a componentwith sections over gaps. Alternatively, in some embodiments, theextruded material might only be cooled while it is being extruded over agap. Without wishing to be bound by theory, selectively cooling materialonly while it is over a gap may lead to better adhesion with previouslydeposited layers of material since the deposited material is at anelevated temperature for a longer period which enhances diffusion andbonding between the adjacent layers.

In the above noted embodiments, a cutting blade is located upstream ofthe nozzle to selectively sever a continuous core when required by aprinter. While that method is effective, there is a chance that atowpreg will not “jump the gap” correctly between the cutting mechanismand the nozzle. Consequently, in at least some embodiments, it isdesirable to increase the reliability of rethreading the core materialafter the cutting step.

As described in more detail below, in some embodiments, a cuttingmechanism is designed to reduce or eliminate the unsupported gap afterthe cutting operation. In such an embodiment, a tube-shaped shear cuttermay be used. As described in more detail below, a towpreg is containedwithin two intersecting tubes that shear relative to each other to cutthe towpreg. In such an embodiment, a gap sufficient to accommodatemovement of the two tilted to each other. The tubes are subsequentlymoved back into alignment to resume feeding the material. In thismechanism there is effectively no gap to jump after the cuttingoperation since the tubes are realigned after cutting. In someembodiments, the gap required for the cutting operation is reduced oreliminated by moving the guide tubes axially together after the cut,thus, eliminating the gap and preventing the fiber from having to jumpthe gap. In other embodiments, and as described in more detail below,the cutting mechanism may be integrated into a tip of a printer headnozzle to eliminate the need for a gap.

FIG. 10 depicts a compression-based continuous-core print head. Asdepicted in the figures, the input material is a towpreg such as acontinuous core filament 2 which is drawn into the feed rollers 40 and42 under tension. To facilitate guiding and maintaining alignment of thecontinuous core filament 2 with the rollers 40 and 42, in someembodiments, the continuous core filament 2 passes through a guide tube74 positioned upstream of the rollers. After passing through therollers, the continuous core filament 2 is placed in compression. Asnoted above, depending on a length of the material under compression aswell as a magnitude of the applied force, the continuous core filament 2may buckle. Consequently, in some embodiments, the continuous corefilament 2 passes through a close-fitting guide tube 72 positioneddownstream of the rollers and upstream of the nozzle. The guide tube 72will both guide and substantially prevent buckling of the continuouscore filament 2. Similar to the above embodiments, a cutting mechanism 8corresponding to a blade is positioned downstream of the guide tube 72.The gap 62 present between the printer head 70 and the cutting mechanism8 is illustrated in the figure. When the continuous core filament 2 iscut by the cutting mechanism 8, the material is “rethreaded” by passingfrom one side of the gap 62 to the other side and into receiving tube64. In some embodiments, the receiving tube 64 is advantageously belowthe glass transition temperature of the material, such that the entiretyof the cutting operation occurs within solid material. In the depictedembodiment, a thermal spacer 66 is located between the receiving tube 64and the hot melt nozzle 68. The thermal spacer 66 reduces the heattransfer to the receiving tube 64 from the hot melting nozzle 68.Similar to the previous embodiment, the continuous-core material 2 isdeposited, layer-by-layer 14 onto a build plate 16. FIG. 11 is aphotograph of a system including the above-noted components.

In some embodiments, the filament used with the device depicted in FIG.10 is provided on a spool 76. When provided in this form, the materialis preformed, substantially solid, and substantially rigid. For example,a preimpregnated core reinforced filament might be provided. Since thematerial has already been formed, it is less likely to stick to thevarious components and/or delaminate during use as might be the case fora green towpreg which may or may not include an uncured resin. Byproviding the filament in a preformed state, the filament is able tosupport compressive forces in addition to being easier to manipulate.This facilitates both handling during threading of the system as well asapplying compressive forces to the material during deposition using acompression-based printer head as described herein.

Without wishing to be bound by theory, the difficulty in jumping the gap62 depicted in FIG. 10 stems from a few key areas. The first difficultyin rethreading is due to the fact that the filament is inherently moreflexible during threading when the end is unsupported, than after it hasbeen threaded and both ends are fully supported and constrained. Morespecifically, the bending mode is second order when rethreaded, which isinherently stiffer, and less prone to bending or buckling, than afilament constrained only at the upstream end corresponding to a firstorder bending mode. Additionally, after the filament has been threaded,the downstream portion serves to guide all the subsequent flowingmaterial into the tube. Finally, cutting a filament introducesdeformation to the feed material which may result in misalignment of thefilament and the receiving tube 64. This misalignment may result in thefilament not appropriately feeding into the receiving tube 64 aftercutting. This deformation can be minimized through the use of stiffmatrix material, and a sharp cutting blade. However, blade wear, and thedesire to use different types of materials, means that in someapplications it may be desirable to use a different cutting mechanism oradditional features to increase threading reliability.

There are several ways to improve the reliability of threading thefilament past a cutting mechanism. For example, in one embodiment, thegap 62 is selectively increased or decreased to permit the introductionof the blade. In such an embodiment, when not in use, the cuttingmechanism 8 is removed from the gap 62 and the guide tube 72 isdisplaced towards the receiving tube 64. This reduces, and in someembodiments, eliminates the gap 62 during rethreading. Alternatively,the guide tube 72 may be constructed and arranged to telescope, suchthat a portion of the guide tube moves towards the receiving tube 64while another portion of the guide tube stays fixed in place to reducethe gap. In another embodiment, rethreading error is reduced using aflow of pressurized fluid, such as air, that is directed axially downthe guide tube 72. The pressurized fluid exits the guide tube 72 at thecutting mechanism 8 as depicted in the figure. Without wishing to bebound by theory, as the continuous core filament 2, or other appropriatematerial, is advanced through gap 62, the axial fluid flow will centerthe material within the fluid flow thus aiding to align the materialwith the receiving end 16. Such an embodiment may also advantageouslyserve to cool the guide tube 72 tube during use. This may helpfacilitate high-speed printing and/or higher printing temperatures. Thefluid flow may also help to reduce friction of the material through theguide tube.

FIG. 12A depicts one embodiment of a shear cutting mechanism. The shearcutting mechanism also eliminates the gap 62 of FIG. 10 which willincrease the reliability of threading. Similar to the above, thecontinuous filament 400 is driven in compression by drive wheel 408, andreceived by a close-fitting guide tube 420. The material is driven incompression through an upper shear cutting block guide 406, lower shearcutting head 402, and heated print head 404. The upper shear cuttingblock 406 and lower shear cutting head 402 are displaced relative toeach other to apply a shearing force to the filament to cut it. While aparticular mechanism has been depicted in the figures, it should beunderstood that any configuration capable of providing a shearing forceto the material might be used. For example, first and second shearingelements may include aligned channels that are shaped and size to accepta filament. The first and/or second shearing elements may then bedisplaced relative to one another to take the channels formed in thefirst and second shearing elements out of alignment and apply a shearforce to the filament to cut it. Additionally, the shear cuttingmechanism may located within a print head, or upstream of the printhead, as the disclosure is not so limited.

FIG. 12B shows the upper shear cutting block 406 translated relative toshear cutting head 402. As noted above, when the upper shear cuttingblock is translated relative to the shear cutting head, the filamentsegment 422 is sheared off from the continuous filament 400. If a simplecut is desired, the shear head 402 can return to the original positionrelative to the upper cutting block 406. In the presented diagram, theupper block moves. However, either block, or both blocks, could movedepending on the particular design. The shear cut and return action isthe simplest cutting formation. After the shear cut and return, the endof the filament 400 is entirely captive in the guiding tube. Therefore,there is no gap to jump, thus, increasing the reliability of feeding thefilament forward for the next section of the part.

In addition to simply performing sheer cutting of a material, in someembodiments, it may be desirable to provide printing capabilities withmultiple types of materials and/or operations. FIG. 12A illustrates oneembodiment of a system including optional indexing stations 414 and 416.When shear head 402 is translated over to either station, a plurality ofuseful operations can additionally occur. In one embodiment, station 416is a cleaning station and includes a cleaning material 410, that can befed through the print head 404 to clean the nozzle. In one example, thematerial is a metal like brass, copper, stainless steel, aluminum, orthe like. This enables the nozzle to be heated, and purged with amaterial having a higher melting temperature than the feed stock. In oneembodiment, the print head 404 is moved to a print cleaning station, forexample, the back corner or other appropriate location. The print head404 is then heated up and indexed to station 416. The cleaning material410 is then fed through the nozzle to clear any obstructions present.The shear cutting action of the upper sheer cutting block 406 and thelower shear cutting head 402 can then sever the sacrificial cleaningpieces to prevent them from being dragged back up the nozzle, andthereby introducing contaminants to the nozzle. In some instances,however, the cleaning agent may be cyclically pushed down, and pulledback up through the nozzle. In another embodiment, the cleaning station416 is used to push any number of cleaning agents such as high-pressureair, liquids, solids, gasses, plasmas, solvents or the like, through thenozzle in order to perform the desired cleaning function.

In addition to the above, in some embodiments, the three-dimensionalprinting system also includes a station 414 corresponding to a differentmaterial 412. Depending on the particular application, the secondmaterial may be an electrically conductive material such as copper, anoptically conductive material such as fiber optics, a second corereinforced filament, plastics, ceramics, metals, fluid treating agents,solder, solder paste, epoxies, or any other desired material as thedisclosure is not so limited. In such an embodiment, the print nozzle404 is indexed from one of the other stations to the station 414 todeposit the second material 412. When the printing function using thesecond material is finished, the print nozzle 404 is then indexed fromstation 414 to the desired station and corresponding material.

FIG. 13 shows a shear cutting block 402 including multiple nozzles 404and 424 formed in the shear cutting block. In one embodiment, the nozzle404 has a larger print orifice than the nozzle 424, enabling largerdiameter towpregs and/or pure polymer materials to be deposited at amore rapid volume. In another embodiment, the second nozzle 424 issubstantially the same as nozzle 404. Consequently, the second nozzle424 may be used as a replacement nozzle that can be automaticallyswitched into use if nozzle 404 becomes clogged. Having an additionalnozzle would decrease the down time of the machine, especially inunattended printing (e.g. overnight). Similar to the above, the firstand second nozzles 404 and 424 may be indexed between differentstations.

FIG. 14A depicts a nozzle 500 including an inlet 502 and an outlet 504.The geometry of the nozzle outlet 504 includes a sharp exit corner.While some embodiments may use a nozzle with a sharp corner at theoutlet, a sharp corner may lead to cutting of fibers in continuous coreprinting. Further, it may scrape off plating of metal cores, andtreatments applied to fiber optic cables incorporated in a core.Consequently, in some embodiments, it is desirable to provide a smoothtransition at an outlet of a nozzle. FIG. 14B depicts a chamfered nozzleoutlet 506, which reduced shear cutting of fibers in testing. Smoothlyrounded nozzle exit 508 advantageously reduces shearing and cutting ofnon-molten continuous cores. It should be appreciated that theparticular design of a transition at an outlet of a nozzle includesaspects such as chamfer angle, fillet angle and degree, length of thetransition, and other appropriate considerations that will varydepending on the particular material being used. For example, Kevlar isextremely strong in abrasion, while fiberglass is weak. Therefore, whilea nozzle including a 45 degree chamfer may be sufficient for Kevlar, itmay result in broken strands when used with fiber glass. However, byusing additional chamfers, or other features, it is possible toeliminate breakage of the fiberglass cores during printing.

As depicted in the figures, nozzle outlet geometries 506 and 508 providea smooth transition from the vertical to the horizontal plane to avoidaccidently cutting the core materials. However, in some embodiments, itmay be desirable to sever the continuous core to cut the filament. Onemethod of severing the continuous core at the tip of the nozzle 500 isto push the nozzle down in the vertical Z direction, as shown by arrow210. As depicted in FIG. 14C, in some embodiments, the corner of thenozzle outlet 508 is sharpened and oriented in the Z direction to enablethe outlet to sever the continuous core as the outlet impinges on andcuts through the material. In order to facilitate cutting of thematerial using such a method, it may be desirable to place the materialunder tension. This tension may be provided in any number of waysincluding, for example, providing a firm hold of the material using thefeeding mechanism, reversing the feeding mechanism and/or moving theprint head. Alternatively, the nozzle 500 might be kept stationary whilethe feeding mechanism is reversed in order to pull the material againstthe edge of the nozzle outlet and cut it. In another embodiment, thecutting can be achieved by simply “breaking” the strand at the cornerpoint where it exits the nozzle by advancing the print head, withoutfeeding, thereby building tension until the core is severed. Typicallythis will occur at the corner point of the nozzle exit. In thisembodiment, a compromise nozzle design may be selected. The nozzle exitgeometry may be slightly sharpened in order to enhance cutting.

In another embodiment, a portion of a nozzle may be sharpened anddirected towards an interior of the nozzle outlet to aid in cuttingmaterial output through the nozzle. As depicted in in FIGS. 15A-15D, anozzle 600 contains a continuous core filament 2, or other appropriatematerial, exiting from a chamfer style nozzle. As depicted in thefigures the nozzle 600 is smoothly chamfered. Additionally, the nozzle600 includes a ring 602 located at a distal outlet of the nozzle. Themajority of the ring 602 is a non-cutting portion of the ring and isshaped and arranged such that it does not interfere with material beingoutput from the nozzle. However, the ring 602 also includes a cuttingportion 602 a which is sharpened and oriented inwards towards thematerial contained within the nozzle 600, see FIGS. 15B-15D. Dependingon the particular embodiment, the cutting portion 602 a is a sharpcutting blade. The cutting portion may be made of a cutting steel, astainless steel, a carbide, a ceramic, or any appropriate material. Asillustrated in FIG. 15D, in some embodiments, the cutting portion 602 aoccupies a fraction of the nozzle outlet area. In such an embodiment,the cutting portion 602 a may either be permanently attached in theindicated position within the nozzle outlet, or it may be selectivelyretracted during the printing process and deployed into a cuttingposition when it is desired to cut the printed material as thedisclosure is not so limited. Alternatively, in other embodiments, thecutting portion 602 a is recessed into a perimeter of the nozzle outletsuch that it does not impinge upon material exiting the nozzle duringnormal operation. For example, the cutting portion 602 a may form a partof the perimeter of the nozzle exit as depicted in FIG. 15C. Otherarrangements of the cutting portion 602 a relative to the nozzle outletare also contemplated. Additionally, while the cutting portion 602 a hasbeen depicted as being incorporated with a ring attached to a nozzle,embodiments in which the cutting portion is either formed with thenozzle outlet and or directly attached to the nozzle outlet are alsocontemplated.

With regards to the embodiment shown in FIGS. 15A-15D, when it isdesired to cut material being extruded from the nozzle, such as, forexample, the continuous core filament 2, the nozzle is translated in adirection D relative to a part being constructed on a surface, see thearrows depicted in the figures. During this translation, the continuouscore filament 2 is not fed through the nozzle. Consequently, thecontinuous core filament 2, and the core contained within it, iseffectively held in place. This results in the tensioning of the corematerial 6 which is displaced towards the cutting portion 602 a throughthe surrounding polymer matrix 4. As increasing tension is applied tothe continuous core filament 2, the core 6 is cut through by the cuttingportion 602 a. Alternatively, in some embodiments, the surface and/orpart is translated relative to the nozzle as the disclosure, or thecontinuous core filament 2 is retracted using the feeding mechanism toapply the desired tension to the core material 6 to perform the severingaction.

While a solid core with a particular size has been depicted in thefigures, it should be understood that the disclosure is not so limited.Instead, such a cutting mechanism may be used with solid cores,multi-filament cores, continuous cores, semi-continuous cores, purepolymers, or any other desired material. Additionally, the core material6 may be any appropriate size such that it corresponds to either alarger or smaller proportion of the material depicted in the figures. Inaddition to the above, for some materials, such as fiber optic cables,the cutting portion 602 a forms a small score in the side the core 6,and additional translation of the nozzle relative to the part completesthe cut. For other materials, such as composite fibers, the roundedgeometry of the nozzle results in the core 6 being directed towards thecutting portion 602 a when it is placed under tension as describedabove. Therefore, the resulting consolidation (e.g. compaction) of thecore towards the cutting portion enables cutting of a large fiber with arelatively smaller section blade. In yet another embodiment, the core 6is either a solid metallic core or includes multiple metallic strands.For example, the core may be made from copper. In such an embodiment,the cutting portion 106 a creates enough of a weak point in the materialthat sufficient tensioning of the core breaks the core strand at thenozzle exit. Again, tensioning of the core may be accomplished throughnozzle translation relative to the part, backdriving of the material, ora combination thereof.

In yet another embodiment, the cutting portion 602 a is a hightemperature heating element that heats the core in order to sever it,which in some applications is referred to as a hot knife. For example,the heating element might heat the core to a melting temperature,carbonization temperature, or to a temperature where the tensilestrength of the core is low enough that it may be broken with sufficienttensioning. It should be understood that, the heating element may heatthe core either directly or indirectly. Additionally, in someembodiments, the element is a high-bandwidth heater, such that it heatsquickly, severs the core, and cools down quickly without impartingdeleterious heat to the printed part. In one particular embodiment, theheating element is an inductive heating element that operates at anappropriate frequency capable of heating the core and/or the surroundingmaterial. In such an embodiment, the inductive heater heats the core toa desired temperature to severe it. Such an embodiment may be used witha number of different materials. However, in one embodiment, aninductive heater is used with a continuous core filament including ametallic core such as copper. The inductive heating element heats themetallic core directly in order to severe the strand. In instances wherethe heating element indirectly heats the core, it may not be necessaryto tension the material prior to severing the core. Instead, the coremay be severed and the nozzle subsequently translated to break thematerial off at the nozzle outlet.

FIG. 16 presents another embodiment of a nozzle tip-based cuttingmechanism m the depicted embodiment, a cutting element 604 is disposedon a distal end of the nozzle 600. While any appropriate arrangementmight be used, in the depicted embodiment a cutting ring disposed aroundthe distal end of the nozzle as depicted in the figure. The cutting ring604 includes a sharp and edge oriented towards the deposited continuouscore filament 2 depicted in the figure. In such an embodiment, thecutting element 604, or a subsection thereof, is actuated downwardstowards the deposited material in order to sever the core of thecontinuous core filament 2. In another version, the internal nozzle 600is translated upwards relative to the cutting element 604. In such anembodiment, the extrusion nozzle 600 may be spring loaded down.Therefore, a cut can be executed by driving the feed head into the part,thereby depressing the inner feed head, relative to the cutting ring,and enabling the cutting ring to sever the core material. In eithercase, the continuous core filament 2 is brought into contact with thecutting element 604, and the core material 6 is severed.

While several different types of cutting mechanisms are described above,it should be understood that any appropriate cutting mechanism capablesevering the core and/or surrounding matrix might be used. Therefore,the disclosure should not be limited to just the cutting mechanismsdescribed here core the particular core material and structure describedin these embodiments.

As noted above, tension-based three-dimensional printing systems exhibitseveral limitations, including the inability to make planar or convexshapes as well as difficulty associated with threading the printedmaterial through the system initially and after individual cuts. Incontrast, a compression-based three-dimensional printing system offersmultiple benefits including the ability to make planar and convex shapesas well as improved threading of the material. However, as notedpreviously, in some modes of operation, and/or in some embodiments,material may be deposited under tension by a system as the disclosure isnot so limited.

Referring again to FIG. 10, a three-dimensional printing system mayinclude a feeding mechanism such as a roller 40 capable of applying acompressive force to the continuous core filament 2 fed into a printerhead 70. However, as noted above, extruding a towpreg, strand, fiber, orother similar material using a compressive force may result in buckling.Consequently, it is desirable to prevent buckling of the material whenit is under compression. Without wishing to be bound by theory,composite fibers are incredibly stiff when constrained in place such aswhen they are held in place by a matrix. However, composite fibers areeasily flexed when dry in a pre-impregnated form when they are notconstrained from moving in off axis directions. Therefore in someembodiments, it is desirable to constrain movement of the material inoff axis directions. While this may be accomplished in a number of ways,in one embodiment, and as noted above, one or more close fitting guidetubes 72 are located between the feeding mechanism and the receivingtube 64 or other inlet of the nozzle. The one or more close fittingguide tubes 72 located along the fiber length help to prevent buckling.The distance between the feeding mechanism, such as the roller 40, andan inlet of the guide tube 72 may be selected to substantially avoidbuckling of the material as well. In some embodiments, it is desirablethat the guide tubes are close fitting and smooth such that their shapeand size are substantially matched to the continuous core filament 2. Inone specific embodiment, the guide tube is a round hypodermic tube.However, embodiments in which the guide tube is sized and shaped toaccept an ovular, square, tape-like material, or any other appropriatelyshaped material are also contemplated. In some embodiments, and asdescribed in more detail below, the continuous core filament 2 mayinclude a smooth outer coating and/or surface, which is in contrast totension wound systems where the core may poke through the outer jacket.This smooth outer surface may advantageously reduce the friction thematerial within the close fitting guide tubes.

In some embodiments, the three-dimensional printing system does notinclude a guide tube. Instead, the feeding mechanism may be locatedclose enough to an inlet of the nozzle, such as the receiving tube 64,such that a length of the continuous core filament 2 from the feedingmechanism to an inlet of the nozzle is sufficiently small to avoidbuckling. In such an embodiment, it may be desirable to limit a forceapplied by the feeding mechanism to a threshold below an expectedbuckling force or pressure of the continuous core filament, or othermaterial fed into the nozzle.

In addition to depositing material using compression, the currentlydescribed three dimensional printers may also be used with compactionpressure to enhance final part properties. For example, FIG. 17A shows acomposite material, such as the continuous core reinforced filament 2,that is extruded through a printer head 60 with an applied compactionforce or pressure 62. The compaction pressure compresses the initialcontinuous core reinforced filament 2 a with an initial shape, see FIG.17B, into the preceding layer below and into a second compacted shape,see FIG. 17C. The compressed continuous core reinforced filament 2 bboth spreads into adjacent strands 2 c on the same layer and iscompressed into the underlying strand of material 2 d. This type ofcompaction is typically achieved in composites through pressure plates,or a vacuum bagging step, and reduces the distance between reinforcingfibers, and increases the strength of the resultant part. While theprinter head 70 may be used to apply a compression pressure directly tothe deposited material other methods of compressing the depositedmaterials are possible. For example the deposited materials might becompacted using: pressure applied through a trailing pressure platebehind the head; a full width pressure plate spanning the entire partthat applies compaction pressure to an entire layer at a time; and/orheat may be applied to reflow the resin in the layer and achieve thedesired amount of compaction within the final part.

As noted above, and referring to FIG. 18A, nozzles 700 used in FusedFilament Fabrication (FFF) three dimensional printers typically employ aconstriction at the tip of the nozzle to trap the solid, non-moltenplastic when it first enters the nozzle at inlet 702 and passes into theheated block 704. The converging nozzle outlet 706 appliesback-pressure, or retarding force, that only enables material to passthrough the nozzle once it has melted, and can squeeze through thesignificantly smaller diameter outlet 706. One of the problemsassociated with Fused Filament Fabrication is the eventual clogging andjamming of the print head (nozzle) due to the convergent nozzle designtrapping material with no means of ejecting it. Further, degradedplastic builds up within the nozzle which eventually clogs the nozzle oralters the extruded print bead. Additionally, in order to clean aconvergent nozzle, the feeding filament must be reversed backwards upthrough the nozzle, potentially contaminating the feed path back to thefilament spool. After reversing through the entire feed path, thecontaminated tip of the feed material must be cut off from the feedspool, and the spool must be re-threaded through the machine. For thesereasons, the nozzles on most FFF three-dimensional printers areconsidered wear items that are replaced at regular intervals.

Having realized these limitations associated with convergent nozzles,the inventors have recognized the benefits associated with a divergentnozzle. In a divergent nozzle, the inflowing material expands as ittransitions from the feed zone, to the heated melt zone, therebyenabling any particulate matter that has entered the feed zone to beejected from the larger heated zone. Additionally, a divergent nozzle isboth easier to clean and may permit material to be removed and a feedforward manner where material is removed through the nozzle outlet ascompared to withdrawing it through the entire nozzle as described inmore detail below.

FIG. 18B shows a nozzle 708 including a material inlet 710, fluidlyconnected to cold-feed zone 712. In the depicted embodiment, the inlet710 and the cold feed zone 712 correspond to a cavity or channel with afirst size and shape. The cold feed zone 712 is disposed on top of himfluidly connected to a heated zone 714. A cross-sectional area of thecavity or channel depicted in the heated zone 714 that is transverse toa path of the filament when positioned therein is greater than across-sectional area of the cavity or channel located in the cold-feedzone 712 that is transverse to the path of the filament. Additionally,in some embodiments, a cross-sectional area of the nozzle outlettransverse to the path of the filament is greater than a cross-sectionalarea of the nozzle inlet transverse to the path of the filament. Thenozzle also includes a nozzle outlet 716. During use, material passesfrom the nozzle inlet 710, through the cold feed zone 712, and into theheated zone 714. The material is then output through the nozzle outlet716. In some embodiments, the cold-feed zone 712 is constructed of amaterial that is less thermally conductive than a material of the heatedzone 714. This may permit the material to pass through the cold feedzone 712 and into the heated zone 714 without softening. In oneparticular embodiment, a divergent nozzle is formed by using alow-friction feeding tube, such as polytetrafluoroethylene, that is fedinto a larger diameter heated zone located within a nozzle such that aportion of the heated zone is uncovered downstream from the tube.Additionally, depending on the embodiment, one or both of the coolfeeding zone and heating zone may be constructed from, or coated with, alow friction material such as polytetrafluoroethylene. While a sharptransition between the cold feed zone and the heated zone has beendepicted in the figures, embodiments of a divergent nozzle in whichthere is a gradual transition from a smaller inlet to a larger outletare also contemplated.

One of the common failure modes of FFF is the eventual creep up of themolten zone into the cold feeding zone, called “plugging”. When the meltzone goes too high into the feed zone, and then cools during printing,the head jams. Having a divergent nozzle greatly reduces the likelihoodof jamming, by enabling molten plastic to be carried from a smallerchannel, into a larger cavity of the divergent nozzle. Additionally, asdescribed below, a divergent nozzle is also easier to clean.

FIG. 18C depicts an instance where a divergent nozzle 708 has beenobstructed by a plug 718 that has formed within the heated zone 714 andbeen removed. Advantageously, a divergent nozzle can be cleaned using aforward-feeding cleaning cycle. In one embodiment, a forward feedingcleaning cycle starts by extruding a portion of plastic onto a print bedsuch that the plastic adheres to the print bed. Alternatively, thesystem may deposit the material onto a cleaning area located at a backof the printing system away from the normal build platform or on anyother appropriate surface as the disclosure is not so limited. Afterattaching to the surface, the system is cooled down to permit thematerial located within the heated zone 714 to cool below the meltingtemperature of the material. After solidification, the print bed andnozzle are moved relative to each other to extract the plug 718 from thenozzle 708. For example, the print bed might be moved down in the zdirection. Alternatively, a printer head including the nozzle might bemoved in a vertical z direction away from the print bed. Additionally,in some embodiments, a feeding mechanism associated with the feedmaterial is driven to apply an additional force to the material as theplug is pulled out of the nozzle. Either way, the plug is then pulledout of the nozzle, advantageously removing debris previously stuck tothe wall, and is done without having to retract the feed material fromthe nozzle through the feed path. While any appropriate material may beused with a divergent nozzle, in some embodiments, a divergent nozzle isused with a material including nylon. This may be beneficial because thecoefficient of thermal expansion for nylon causes it to pull away fromthe nozzle slightly during cooling and nylons exhibit low coefficient offriction. Again, the use of polytetrafluoroethylene within one, or bothof the cold feed zone and the heated zone, may help facilitate the easyremoval of plugs formed within the nozzle.

While a method of use in which the divergent nozzle is cleaned byattaching a plug to a surface, in another embodiment, a cleaning cycleis performed by simply extruding a section of plastic into free air. Theplastic may then be permitted to cool prior to being removed by hand orusing an automated process. When the material is removed, any plugattached to that material is also removed.

In another embodiment, a forward feeding cleaning cycle is used with aslightly convergent nozzle. For example, convergent nozzles with anoutlet to inlet ratio of 60% or more might be used, though other outletto inlet ratios are also possible. The forward extrusion cleaning methodfor such a nozzle includes extruding a section of molten material, andoptionally attaching it to the print bed. The heated nozzle is thenallowed to cool. During the cooling process, the ejected portion ofmaterial is pulled such that the material located within the heated zoneis stretched, thereby reducing a diameter of the material. The materialmay be stretched to a degree such that the diameter of the materiallocated within the heated zone is less than a diameter of the nozzleoutlet. Additionally, once the material has cooled, further pullingenables diameter contraction through the Poisson's ratio of thematerial, thereby further facilitating removal of the remnant locatedwithin the nozzle. In some embodiments, the material is stretched byapplying a force by hand, or other external means, to the extrudedmaterial. In other embodiments where the material is attached to asurface, the printer head and/or surface are displaced relative to eachother as noted above to apply a force to the material to provide thedesired structure. The above described method enables the feed forwardcleaning of a slightly convergent nozzle to be cleaned with forwardmaterial flow.

While a divergent nozzle has been discussed above, embodiments in whicha straight nozzle is used for FFF printing are also contemplated. FIG.19A depicts a nozzle 720 including an inlet 724 that is substantiallythe same size as nozzle outlet 722. A material such as a continuous corefilament 2 passes through a cold feed zone 712 and into a heated zone714. In one embodiment, the cold feed zone is a low friction cold-feedzone made from a material with a low coefficient of thermal conductionsuch as polytetrafluoroethylene. Correspondingly, the heated zone 714 ismade from a more thermally conductive material such as copper, stainlesssteel, brass, or the like. Regardless of the specific construction,after melting, the continuous core filament 2 is deposited on, andattached to, a build platen 16 or other appropriate surface. Straightnozzles are ideally suited to small diameter filaments, on the order ofabout 0.001″ up to 0.2″. However, embodiments in which materials withdiameters both greater than and less than those noted above are usedwith a substantially straight nozzle are also contemplated. Withoutwishing to be bound by theory, the low thermal mass associated withthese small filaments permits them to heat up quickly. Additionally, thesmall dimensions permit these materials to be extruded at substantiallythe same size as they are fed into the print head. Similar to adivergent nozzle, a substantially straight nozzle offers the advantagesof forward feeding cleaning cycles that enables a cooled plug to beremoved from the tip and substantially avoiding collecting particles anddebris within the nozzle.

A nozzle similar to that described in FIG. 19A can also be used with atypical green towpreg 734. However, this may result in clogging similarto typical three dimensional printing systems using a green towpreg. Theclogging is a result of trying to “push” a flexible composite strandthrough a nozzle in the initial stitching operation. FIG. 19Billustrates what happens when a green towpreg is output through nozzle720 during an initial stitching operation to attach it to a part orbuild plate. Namely, instead of being pushed through the nozzle asintended, the individual fibers in the green towpreg 734 tend to stickto the walls of the nozzle and commensurately start to bend and curl upat 736. Put another way, the flexible fibers located within a green orflexible towpreg are likely to delaminate and become clogged in thenozzle. Flexible materials may include, but are not limited to, a moltenthermoplastic and/or un-cured plastic for two part mixed epoxy or lasercured resins, though other flexible materials are also possible.

In contrast to the above, a stitching process associated with apreimpregnated continuous core filament within a divergent nozzle doesnot suffer the same limitations. More specifically, FIGS. 19C-19Eillustrate a method of stitching using a rigid preimpregnated continuouscore filament fed through a divergent nozzle, such that clogging isreduced, or substantially eliminated. FIG. 19C shows a continuous corefilament 2 located within the cold feed zone 712. Depending on theparticular embodiment, the material may be located on the order of 5inches or more from the heated zone 714, though other distances are alsocontemplated. Additionally, in embodiments where the material has alarger thermal capacity and/or stiffness, it may be located closer tothe heated zone 714 to provide pre-heating of the material prior tostitching. While located within the cold feed zone 712, which is below amelting temperature of the matrix, the continuous core filament 2remains substantially solid and rigid. The continuous core filament 2 ismaintained in this position until just prior to printing. At that point,the continuous core filament 2 is quickly stitched through the nozzle,i.e. displaced through the nozzle outlet, see FIG. 19D. Since thecold-feed zone 712 feeds into a larger cavity corresponding to theheated zone 714, when the material is stitched, the continuous corefilament 2 is constrained from touching the walls of the heated zone 714by portion of the filament still located in the outlet of the cold feedzone, see FIG. 19D. By performing the stitching quickly, melting of thematrix may be minimized to maintain a stiffness of the compositematerial. By maintaining a stiffness of the material and preventingmelting until the material has been stitched, it is possible to preventfibers from peeling off, curling and/or clogging within the nozzle. Thismay enable the feed material to be more easily pushed into, and through,the hot-melt zone. In some embodiments, a blast of compressed air may beshot through the nozzle prior to and/or during stitching in order tocool the nozzle to reduce the chance of sticking to the sides of thenozzle. Additionally, heating of the heated zone 714 of the nozzle maybe reduced or eliminated during a stitching process to also reduce thechance of sticking to the sides of the nozzle.

As feeding of the continuous core filament 2 continues, the continuouscore filament 2 eventually contacts the build platen 16, or otherappropriate surface. The continuous core filament 2 is then draggedacross the surface by motion of the nozzle relative to the build platen16. This results in the continuous core filament 2 contacting the wallsof the heated zone 714 as illustrated in FIG. 19E. Alternatively,instead of translating the printer head, the material could be driven toa length longer than a length of the nozzle. When the outlet of thenozzle is blocked by a previous layer of the part, or by the print bed,the material will buckle and contact the walls of the heated zone 714.Regardless of the particular method employed, after contacting the wallsof the heated zone 714, the continuous core filament 2 is heated up to adesired deposition temperature capable of fusing the deposited materialto a desired surface and/or underlying previously deposited layers thusenabling three-dimensional printing. For example, once translation ofthe print head begins, the matrix material contacts a wall of the heatedzone and is heated to a melting temperature of the matrix material.Stitching speeds obtained with a system operated in the manner describedabove, was capable of stitching speeds between about 2500 mm/min and5000 mm/min. However, the stitching speed will vary based on nozzleheating, matrix material, and other appropriate design considerations.While a particular stitching method has been described above, it shouldbe noted that other types of stitching and melting techniques could alsobe employed as the disclosure is not limited to any particulartechnique.

As also depicted in FIGS. 19C-19E, in some embodiments, the nozzle 708may include a rounded or chamfered lip 726, or other structure, locatedat a distal end of the nozzle outlet 716. This may serve two purposes.First, as noted previously, a gradual transition at the nozzle outletmay help to avoid fracturing of the continuous core. Additionally, insome embodiments, the lip 726 is positioned such that the lip applies adownward force to the continuous core filament 2 as it is deposited.This may in effect applying a compaction force to the material as it isdeposited which may “iron” the continuous core filament down to theprevious layer. As noted above compaction forces applied to the materialmay offer multiple benefits including increased strength and reducedvoid space to name a few. This compaction force may be provided bypositioning the lip 726 at a distance relative to a deposition surfacethat is less than a diameter of the continuous core filament 2. However,compaction forces provided using distances greater than a diameter ofthe continuous core filament are also possible for sufficiently stiffmaterials. This distance may be confirmed using an appropriate sensor,such as a range finder as noted above. In some embodiments, the lip 726is incorporated with a substantially straight nozzle 720 or a slightlyconvergent nozzle as the disclosure is not so limited, see FIG. 20A.

While the above embodiments have been directed to divergent and straightnozzles including a cold feed zone and a separate heated zone,embodiments in which a convergent nozzle includes a separate cold feedzone and heated zone are also contemplated. For example, FIG. 20B showsan nozzle 728 including a nozzle inlet 730 that feeds into a cold feedzone 712 which is in fluid communication with a heated zone 714. Theheated zone 714 is incorporated with a convergent nozzle outlet 732.

In embodiments using a high-aspect ratio convergent nozzle, it may bedesirable to use a nozzle geometry that is optimized to prevent thebuildup of feed material and/or to reduce the required feed pressure todrive the material through the nozzle outlet. FIG. 21A shows a typicalFFF nozzle 800 including an inlet 806 that is aligned with an internalwall 802. The internal wall 802 extends up to a convergent section 804that leads to a nozzle outlet 808 with an area that is less than an areaof the inlet 806. FIGS. 21B-21D depict various geometries includingsmooth transitions to reduce a back pressure generated within thenozzle.

In one embodiment, as depicted in FIG. 21B, a nozzle 810 includes aninlet 806 and an internal wall 812 with a first diameter. Initially, theinternal wall 812 is vertical and subsequently transitions to atangential inward curvature 814. After about 45 degrees of curvature, aninflection point 816 occurs and the internal wall reverses curvature andcurves until the internal wall 812 is vertical. The resulting nozzleoutlet 818 is aligned with the inlet 810, but has a reduced seconddiameter. Additionally, the resulting exit flow from the outlet will bealigned with the inlet flow, though flows through the outlet that arenot aligned with the inlet are also contemplated.

When a lower degree of alignment of polymer chains is desirable, thefirst inward curving section 814 depicted in FIG. 21B can be eliminated,such that the final geometry that turns the flow back into the extrudeddirection does so after a more typical chamfered inlet. One suchembodiment is depicted in FIG. 21C. As depicted in the figure, a nozzle820 includes an internal wall that transitions to a downwards orientedcurvature 822 directed towards the nozzle outlet 824. FIG. 4D depictsanother embodiment in which a nozzle 826 transitions to a standardchamfered nozzle section 828 which extends up to a point 830 where ittransitions to a downwards oriented curvature 832 to define a nozzleoutlet 834. While particular nozzle geometries have been depicted infigures and described above, should be understood that other types ofnozzle geometries might also be used as the disclosure is not solimited.

In some embodiments, a nozzle includes one or more features to preventdrips. For example, a nozzle may include appropriate seals such as oneor more gaskets associated with a printing nozzle chamber to prevent theinflow of air into the nozzle. This may substantially prevent materialfrom exiting the nozzle until material is actively extruded using afeeding mechanism. In some instances, it may be desirable to includeother features to prevent dripping from the nozzle as well whileprinting is stopped. In one specific embodiment, a nozzle may include acontrollable heater that can selectively heat the nozzle outlet toselectively start and stop the flow of material form the nozzle. In thisregard, a small amount of the resin near the outlet may solidify whenthe heater is power is reduced to form a skin or small plug to preventdrooling from the outlet. Upon reenergizing or increasing the heaterpower, the skin/plug re-melts to allow the flow of material from thenozzle. In another embodiment, the nozzle includes features toselectively reduce the pressure within the nozzle to prevent dripping.This can be applied using a vacuum pump, a closed pneumatic cylinder, orother appropriate arrangement capable of applying suction when nozzledripping is undesirable. The pneumatic cylinder is then returned to aneutral position, thus eliminating the suction, when printing isresumed. FIG. 22 depicts one such embodiment. In the depictedembodiment, an extrusion nozzle 900 has a material 902 that is fed pastone or more gaskets 910 and into a cold feed zone 914 and heated zone912 prior to exiting nozzle outlet 908. An air channel 904 is connectedto the cold feed zone 914 and is in fluid communication with a pneumaticcylinder 906. As depicted in the figure, a gap is present between thematerial 902 and the cold feed zone 914 through which air may pass.Therefore, the air channel 904 is in fluid communication with both thecold feed zone 914 as well as with material located within the heatedzone 912. During operation, the pneumatic cylinder 906 is actuated froma first neutral position to a second position to selectively applyingsuction to the air channel 904 when printing is stopped. Since the airchannel 904 is in fluid communication with material within the heatedzone 912, the suction may substantially prevent dripping of polymer meltlocated within the heated zone. Once printing resumes, the pneumaticcylinder 906 may be returned to the neutral position.

While various embodiments of nozzles in cutting mechanisms are describedabove, in some embodiments, it is desirable to use a towpreg, or othermaterial, that does not require use of a cutting mechanism to cut. Inview of the above, the inventors have recognized the benefits associatedwith using a material including a semi-continuous core strand compositewith a three-dimensional printer. In such an embodiment, a materialincluding a semi-continuous core has a core that has been divided intoplurality of discrete strands These discrete strands of the core mayeither correspond to a solid core or they may correspond to a pluralityof individual filaments bundled together as the disclosure is not solimited. Additionally, as described in more detail below, these discretesegments of the core may either be arranged such that they do notoverlap, or they may be arranged in various other configurations withinthe material. In either case, the material may be severed by applying atension to the material as described in more detail below. The tensionmay be applied by either backdriving a feed mechanism of the printerand/or translating a printer head relative to a printed part withoutextruding material from the nozzle.

In one embodiment a material including semi-continuous core includessegments that are sized relative to a melt zone of an associatedthree-dimensional printer nozzle such that the individual strands may bepulled out of the nozzle. For example, the melt zone could be at leastas long as the strand length of the individual fibers in a pre-pregfiber bundle, half as long as the strand length of the individual fibersin a pre-preg fiber bundle, or any other appropriate length. In such anembodiment, at the termination of printing, the material including asemi-continuous core is severed by tensioning the material. Duringtensioning of the material, the strands embedded in material depositedon a part or printing surface provide an anchoring force to pull out aportion of the strands remaining within the nozzle. When the individualstrands are appropriately sized relative to a melt zone of the nozzle asnoted above, strands that are located within both the extruded materialand with the nozzle are located within the melt zone of the nozzle.Consequently, when tension is applied to the material, the segmentslocated within the melt zone are pulled out of the melt zone of thenozzle to sever the material. In embodiments where longer strands areused, instances where at least some strands are pulled out of a moltenzone of the deposited material and retained within the nozzle are alsocontemplated. The above noted method may result in vertically orientedstrands of core material. This vertical strands may optionally be pushedover by the print head, or they are subsequently deposited layers. Bystrategically placing vertically oriented strands within a materiallayer, it may be possible to increase a strength of the resulting partin the z direction by providing enhanced bonding between the layers.

In another embodiment, a semi-continuous core embedded in acorresponding matrix material includes a plurality of strands that havediscrete, indexed strand lengths. Therefore, termination of thesemi-continuous core occurs at pre-defined intervals along the length ofthe material. Initially, since the terminations are located atpredefined intervals, the strand length may be larger than a length ofthe melt zone of an associated nozzle. For example, in one specificembodiment, a semi-continuous core might include individual strands, orstrand bundles, that are arranged in 3-inch lengths and are cleanlyseparated such that the fibers from one bundle do not extend into thenext. When using such a material, a three-dimensional printer may run apath planning algorithm to lineup breaks in the strand with naturalstopping points in the print. In this embodiment, there is a minimumfill size which scales with the semi-continuous strand length becausethe printer cannot terminate the printing process until a break in thesemi-continuous strand is aligned with the nozzle outlet. Therefore, asthe strand length increases, in some embodiments, it may be advantageousto fill in the remainder of the layer with pure resin which has nominimum feature length. Alternatively, a void may be left in the part.In many geometries, the outer portion of the cross section provides morestrength than the core. In such cases, the outer section may be printedfrom semi-continuous strands up until the last integer strand will notfit in the printing pattern, at which point the remainder may be leftempty, or filled with pure resin.

In another embodiment, a material may include both of the aboveconcepts. For example, indexed continuous strands may be used, inparallel with smaller length bundles located at transition pointsbetween the longer strands, such that the melt zone in the nozzleincludes sufficient distance to drag out the overlapping strands locatedin the melt zone. The advantage of this approach is to reduce the weakpoint at the boundary between the longer integer continuous strands.During severance of a given core and matrix material, it is desirablethat the severance force is sufficiently low to prevent part distortion,lifting, upstream fiber breaking, or other deleterious effects. In somecases, strands may be broken during the extraction, which is acceptableat the termination point. While the strand length can vary based on theapplication, typical strand lengths may range from about 0.2″ up to 36″for large scale printing.

FIGS. 23A-24D depict various embodiments of a semi-continuous corefilament being deposited from a nozzle. As contrasted to the continuouscore filament 2 depicted in FIG. 24A.

As depicted in the FIG. 23A, a semi-continuous core filament 1000including a first strand 1002 and a second strand 1004 located withinthe matrix material 1006. The semi-continuous core filament 1000 entersa cold feeding zone 712 of a nozzle which is advantageously below theglass transition temperature of the matrix material. The semi-continuousmaterial 1000 subsequently flows through heated zone 714, sometimesreferred to as a melt zone. The matrix material 1006 present in thesemi-continuous material 1000 is melted within the heated zone 714 priorto deposition. Upon exit from the nozzle, semi-continuous core filament1000 is attached to a part or build platen 16 at anchor point 1005. Theseverance procedure can then occur in a number of ways. In oneembodiment, severance occurs by moving the print head forward relativeto the anchor point 1005, without advancing the semi-continuous corefilament 1000. Alternatively, the print head may remain stationary, andthe upstream semi-continuous core filament 1000 is retracted to applythe desired tension. Again by appropriately sizing the strand length toa length of the heated zone to ensure that an entire length of thestrand located within the nozzle is in the heated zone 714, the tensionprovided by the anchor point 1005 permits the remaining portion of thesecond strand 1004 located within the nozzle to pull the remnant of theembedded strand from the heated nozzle.

While FIG. 23A showed two individual strands, FIGS. 23B and 24B show asemi-continuous core filament 1008 including a distribution of similarlysized strands 1010 embedded in a matrix material 1006 and located in aprinter head similar to that described above. While three strands areshown in a staggered line, it should be understood that this is asimplified representation of a random, or staggered, distribution ofstrands. For example, material may include about 1,000 strands of carbonfiber (a lk tow). While a distribution of strand lengths 1015 andpositioning of the individual strands is to be expected, the strands 214may be sized and distributed such that there are many overlappingstrands of substantially similar length. By ensuring that heated zone714 is proportional to a strand length 1015, the fiber remnant can bemore easily pulled from the nozzle. For example, and without wishing tobe bound by theory, the strands that are located further downstream,i.e. mostly deposited within a part, will pull out from the nozzleeasily. The strands that are mostly located in the nozzle will mostlikely remain within the nozzle. The strands that are half in thenozzle, and half out, will stochastically stay in the nozzle or getpulled out by the anchor point 1005 due to the roughly equivalent forcesbeing applied to roughly equivalent lengths of the strands containedwithin the deposited material and the nozzle. The various parameters ofthe nozzle design such as the design of the cold feeding zone 714 andthe nozzle outlet transition as well as the viscosity of the polymermelt, the degree of cooling of the printed semi-continuous core filamentupon exit from the nozzle outlet, as well as other appropriateconsiderations will determine how the semi-continuous core filament issevered when a tension is applied to the material.

FIGS. 23C and 24C shows an indexed semi-continuous core filament 1012where the termination of the core material is substantially complete ateach section, thereby enabling clean severance at an integer distance.As depicted in the figures, the material includes individual sections ofone or more core segments 1014 embedded within a matrix material 1006.The individual sections of core material are separated from adjacentsections of core material at pre-indexed locations 1016. Such anembodiment advantageously permits the clean severance of the material ata prescribed location. This is facilitated by the individual strands indifferent sections not overlapping with each other. This also enablesthe use of strand lengths that are larger than a length of theassociated heated zone 714 of the nozzle. This also permits use of thesmaller heated zone 714 in some embodiments. However, in addition to thenoted benefits, since the individual strands in different sections donot overlap, the material will exhibit a reduced strength at theseboundary locations corresponding to the pre-indexed locations 1016depicted in the figures. FIG. 25 illustrates the use of such asemi-continuous core filament. As depicted in the figure, multiplestrands 1100 are deposited onto a part or build platen. The strands 1100are deposited such that they form turns 1102 as well as other featuresuntil the print head makes it final pass and severs the material at 1104as described above. Since the individual strands are longer than theremaining distance on the part, the remaining distance 1106 may eitherbe left as a void or filled with a separate material such as a polymer.

FIG. 24D shows an example of a hybrid approach between a semi-continuouscore filament and a continuous core filament. In the depictedembodiment, a material 1018 includes multiple discrete sectionsincluding one or more core segments 1014 embedded within a matrix 1006that are located at pre-indexed locations similar to the embodimentdescribed above in regards to FIGS. 24C and 25C. The material alsoincludes a continuous core 1020 embedded within the matrix 1006extending along a length of material. The continuous core 1020 may besized such that it may be severed by a sufficient tensile force toenable severing of the material at the pre-indexed locations simply bythe application of a sufficient tensile force. Alternatively, any of thevarious cutting methods described above might also be used.

While the above embodiments have been directed to materials that may besevered without the use of a cutting mechanism. It should be understoodthat semi-continuous core filaments may also be used with threedimensional printing systems including a cutting mechanism as thedisclosure is not so limited.

In traditional composite construction successive layers of compositemight be laid down at 0°, 45° 90° and other desired angles to providethe part strength in multiple directions. This ability to control thedirectional strength of the part enables designers to increase thestrength-to-weight ratio of the resultant part. Therefore, in anotherembodiment, a controller of a three dimensional printer may includefunctionality to deposit the reinforcing fibers with an axial alignmentin one or more particular directions and locations. The axial alignmentof the reinforcing fibers may be selected for one or more individualsections within a layer, and may also be selected for individual layers.For example, as depicted in FIG. 26 a first layer 1200 may have a firstreinforcing fiber orientation and a second layer 1202 may have a secondreinforcing fiber orientation. Additionally, a first section 1204 withinthe first layer 1200, or any other desired layer, may have a fiberorientation that is different than a second section 1206, or any numberof other sections, within the same layer.

The concept of providing axial orientation of the reinforcing fibers toprovide directional strength within the part may be taken further withthree dimensional printers. More specifically, FIGS. 27A-27C show amethod of additive manufacturing of an anisotropic object with a printerhead 1310, such as an electric motor or other part that may benefit fromanisotropic properties. In the depicted embodiment, a part 1300 has avertically oriented subcomponent 1302 that is printed with the partoriented with Plane A aligned with the XY print plane in a firstorientation. In this particular example, the printed material includes aconductive core such that the printed subcomponent 1302 forms a woundcoil of a motor. In the depicted embodiment, the coils are wound aroundthe Z direction. While a particular material for use in printing a motorcoil is described, it should be understood that other materials might beused in an anisotropic part for any number of purposes as the currentdisclosure is not limited to any particular material or application.

In order to form another coil, or other anisotropic subcomponent, on thepart 1300, a fixture 1304, shown in FIG. 27B, is added to the print areathough embodiments in which this feature is printed during, before, orafter the formation of part 1300 are also possible. In one embodiment,the fixture 1304 is positioned at, or below, the print plane 1306 and iscontoured to hold the part 1300 during subsequent deposition processes.The fixture may also include vacuum suction, tape, mechanical fasteners,printed snap fits, or any other appropriate retention mechanism tofurther hold the part during subsequent print processes.

After positioning the fixture 1304, the part 1300 is positioned onfixture 1304, which then holds the part 1300 in a second orientation,with plane A rotated to plane A′ such that the next subcomponent 1308can be added to the part 1300. The subcomponent 1308 is again depositedin the Z direction, but is out of plane with subcomponent 1302, as shownin FIG. 27C. While this example has been described with regards toforming the coiled windings of a motor, any anisotropic object could beformed using a series of fixture rotations of the part, or print head,to enable the continuous core reinforced filaments to be aligned in anoptimal direction for various purposes.

FIG. 28A shows the same anisotropic part as formed in the processdescribed in FIGS. 27A-27C, however, instead of making use of aplurality of fixtures, the three dimensional printer is capable ofrotating the part 1300 as well as the printer head 1310 about one ormore axes. As depicted in the figure, part 1300 is held in place by arotating axis 1312, which sets and controls the orientation of plane A.In FIG. 28B, rotating axis 1312 has been rotated by 90° to formsubcomponent 1308 in a direction that is perpendicular to subcomponent1302. Conversely, printer head 510 could be pivoted about the XT and/oryT axes to achieve a similar result. As FIGS. 28A-28B show, there aremany ways to achieve anisotropic printing. Namely, the part may be movedand rotated, the printer head may be moved and rotated, or a combinationof both may be used to print an anisotropic part. It should beunderstood, that additional degrees of freedom could be added to eitherthe rotation and movement of the part 1300 or the printer head 1310based on the machine objectives, and part requirements. For example, inan automotive application, rotating axis 1312 may correspond to arotisserie, enabling rotation of the vehicle frame about the yT axis toenable continuous fibers to be laid in the X-Y plane, the Z-Y plane, orany plane in between. Alternatively, a fluid rotation following theexternal contours of the vehicular body might be used to continuouslydeposited material on the vehicle as it is rotated. Such a threedimensional printer might optionally add the XT axis to the printer headto enable full contour following as well as the production of bothconvex and concave unibody structures.

In addition to rotating the part 1300 and the printer head 1310, in someembodiments, a table 1314 supporting the part 1300 could be rotatedabout the zT axis to enable spun components of a given fiber direction.Such an embodiment may provide a consistent print are from the printhead to the part for core materials that have unique feeding anddeposition head requirements that prefer directional consistency.

In another embodiment, the core of a part may be built up as a series oftwo dimensional planes. The three-dimensional printer may then form, outof plane three dimensional shells over the interior core. The coresupports the shells which enables the shells to be constructed on theoutside of the core and may run up the sides of the part, over the top,and/or down the back sides of the part, or along any other location.Without wishing to be bound by theory, such a deposition method may aidin preventing delimitation and increase torsional rigidity of the partdue to the increased part strength associated with longer and morecontinuous material lengths. Further running the continuous fiberreinforced materials out of plane provides an out-of-plane strength thatis greater than a typical bonded joint.

FIG. 29 shows a three dimensional printer head 1310 similar to thatdescribed above in regards to FIGS. 28A and 28B that can be used to forma part including a three dimensionally printed shell. The printer head1310 deposits any appropriate consumable material such as a continuouscore reinforced filament 2 onto the built platen 1314 in a series oflayers 1320 to build a part. The printer head 1310 is capable ofarticulating in the traditional XYZ directions, as well as pivoting inthe XT yT and zT directions. The additional degrees of freedom to pivotthe printer head 1310 allow the printer to create shells, and othercontiguous core reinforced out of plane layers, as well as twodimensional layers.

FIGS. 30A-30C depict various parts formed using the printer headdepicted in FIG. 29. FIG. 30A shows a part including a plurality ofsections 1322 deposited as two dimensional layers in the XY plane.Sections 1324 and 1326 are subsequently deposited in the ZY plane togive the part increased strength in the Z direction. FIG. 30B show arelated method of shell printing, where layers 1328 and 1330 are formedin the XY plane and are overlaid with shells 1332 and 1334 which extendin both the XY and ZY planes. As depicted in the figure, the shells 1332and 1334 may either completely overlap the underlying core formed fromlayers 1328 and 1330, see portion 1336, or one or more of the shells mayonly overly a portion of the underlying core. For example, in portion1338 shell 1332 overlies both layers 1328 and 1330. However, shell 1334does not completely overlap the layer 1328 and creates a steppedconstruction as depicted in the figure. FIG. 30C shows anotherembodiment where a support material 1340 is added to raise the partrelative to a build platen, or other supporting surface, such that thepivoting head of the three dimensional printer has clearance between thepart and the supporting surface to enable the deposition of the shell1342 onto the underlying layers 1344 of the part core.

The above described printer head may also be used to form a part withdiscrete subsections including different orientations of a continuouscore reinforced filament. For example, the orientation of the continuouscore reinforced filament in one subsection may be substantially in theXY direction, while the direction in another subsection may be in the XZor YZ direction. Such multi-directional parts enable the designer to runreinforcing fibers exactly in the direction that the part needsstrength.

The high cost of composite material has been one of the major barriersto widespread adoptions of composite parts. Therefore, in someembodiments a three dimensional printer may utilize a fill pattern thatuses high-strength composite material in selected areas and fillermaterial in other locations, see FIGS. 30D-300. Consequently, incontrast to forming a complete composite shell on a part is describedabove, a partial composite shell is formed on the outer extremes of apart, to maximize the stiffness of the part for a given amount ofcomposite material used. Low-cost matrix material such as nylon plasticmay be used as the fill-in material, though other materials may also beused. A part formed completely from the fill material 1350 is depictedin FIG. 30D. As illustrated in FIG. 30E, a composite material 1352 isdeposited at the radially outward most portions of the part andextending inwards for a desired distance to provide a desired increasein stiffness and strength. The remaining portion of the part is formedwith the fill material 1350. Alternatively, portions of the build planemay be left unfilled. Depending on the desired strength and/orstiffness, a user may increase or decrease an amount of the compositematerial 1352 used. This will correspond to the composite materialextending either more or less from the various corners of the part. Thisvariation in amount of composite material 1352 is illustrated by theseries of figures FIGS. 30D-300.

When determining an appropriate fill pattern for a given level ofstrength and stiffness, a control algorithm starts with a concentricfill pattern that traces the outside corners and wall sections of thepart, for a specified number of concentric infill passes, the remainderof the part may then be filled using a desired fill material. Theresultant structure maximizes the strength of the part, for a minimum ofcomposite usage. It should be understood that while the above process isdescribed for a two dimensional plane, it is also applicable to threedimensional objects as well.

FIGS. 31A-31C show the cross-sections of various embodiments of anairfoil with different fiber orientations within various subsections. Itshould be understood that while an airfoil as described below, thedescribed embodiments are applicable to other applications andconstructions as well.

FIG. 31A shows a method of building each section of the threedimensional part with plastic deposition in the same plane.Specifically, sections 1350, 1352 and 1354 are all constructed in thesame XY planer orientation. The depicted sections are attached at theadjoining interfaces, the boundary of which is exaggerated forillustration purposes. In another embodiment, and as depicted in FIG.31B, a part is constructed with separate sections 1362, 1364, and 1366where the fiber orientations 1368 and 1372 of sections 1362 and 1366 areorthogonal to the fiber orientation 1370 of section 1364. Withoutwishing to be bound by theory, by orthogonally orienting the fibers insection 1364 relative to the other sections, the resulting part has amuch greater bending strength in the Z direction. Further, byconstructing the part in this manner, the designer can determine therelative thickness of each section to prescribe the strength along eachdirection.

FIG. 31C depicts a shell combined with subsections including differentfiber orientations. In this embodiment, sections 1374, 1376, and 1378are deposited in the same direction to form a core, after which a shell1386 is printed in the orthogonal direction. The shell 1386 may be asingle layer or a plurality of layers. Further, the plurality of layersof shell 1386 may include a variety of orientation angles other thanorthogonal to the underlying subsections of the core, depending on thedesign requirements. While this embodiment shows the inner sections withfiber orientations all in the same direction 1380, 1382, and 1384, itshould be obvious that subsections 1374, 1376, and 1378 may be providedwith different fiber orientations similar to FIG. 31B as well.

In other embodiments, the continuous core reinforced filament, or otherappropriate consumable material, may require a post-cure, such that thepart strength is increased by curing the part. Appropriate curing may beprovided using any appropriate method including, but not limited to,heat, light, lasers, and/or radiation. In this embodiment, a part may beprinted with a pre-preg composite and subject to a subsequent post-cureto fully harden the material. In one specific embodiment, continuouscarbon fibers are embedded in a partially cured epoxy such that theextruded component sticks together, but requires a post-cure to fullyharden. It should be understood that other materials may be used aswell.

FIG. 32 depicts an optional embodiment of a three dimensional printerwith selectable printer heads. In the depicted embodiment, a print arm1400 is capable of attaching to printer head 1402 at universalconnection 1404. An appropriate consumable material 1406, such as acontinuous core reinforced filament, may already be fed into the printerhead 1402, or it may be fed into the printer after it is attached to theprinter 1400. When another print material is desired, print arm 1400returns printer head 1402 to an associated holder. Subsequently, theprinter 1400 may pick up printer head 1408 or 1410 which are capable ofprinting consumable materials that are either different in size and/orinclude different materials to provide different. As depicted, suchswappable printer heads are used one at a time, and advantageouslyreduce the mass of the printer head and arm combination. Without wishingto be bound by theory, this enables faster printing of a part due to thereduced inertia of the printer head. In another embodiment, the printarm may have slots for two or more printer heads concurrently. Suchheads may feed different material, apply printed colors, apply a surfacecoating of spay deposited material, or the like. It should be understoodthat any number of separate selectable print heads might be provided.For example, the print heads may be mounted to a turret, with one printhead in the “active” position and the others rotated out of positionawaiting for the appropriate time when they may be rotated into theprint position. In another embodiment, print arm may 1400 pick up avision system 1412 for part inspection. Appropriate vision systemsinclude cameras, rangefinders, or other appropriate systems.

While most of the above embodiments are directed to the use of preformedcontinuous core reinforced filaments, in some embodiments, thecontinuous core reinforced filament may be formed by combining a resinmatrix and a solid continuous core in the heated extrusion nozzle. Theresin matrix and the solid continuous core are able to be combinedwithout the formation of voids along the interface due to the ease withwhich the resin wets the continuous perimeter of the solid core ascompared to the multiple interfaces in a multifilament core. Therefore,such an embodiment may be of particular use where it is desirable toalter the properties of the deposited material. Further, it may beespecially beneficial to selectively extrude one or more resin matrices,continuous cores, or a combination thereof to deposit variety of desiredcomposite structures.

FIG. 33 depicts a multi-element printer head 1500 that is capable ofselectively extruding material feed options 1502, 1504, and 1506 as wellas an optional cutting mechanism 8. More specifically, the multi-elementprinter head 1500 is capable of selectively depositing any of materialfeed options 1502, 1504, and 1506, as singular elements or incombination. It should be understood that other material feed optionsmay also be integrated with the multi-element printer head as thecurrent disclosure is not limited to any particular number of materialfeed options.

In one specific example of a multi-element printer head, material 1502is a continuous copper wire fed through a central channel. Further,material 1504 is a binding resin such as Nylon plastic and material 1506is a different binding resin such as a dissolvable support material. Themulti-element printer head 1500 is capable of extruding all the elementsat once where, for example, the copper wire 1502 might be surrounded bythe nylon binder 1504 on the bottom surface and the dissolvable supportmaterial 1506 on the top surface, see section 1508. The multi-elementprinter head 1500 may also deposit the copper wire 1502 coated witheither the nylon binder 1504 or the soluble support material 1506separately, see sections 1510 and 1514. Alternatively, the multi-elementprinter head 1500 can deposit the above noted material options singlyfor any number of purposes, see the bare copper wire at section 1512.

The ability to selectively deposit any of the one or more of thematerials in a given location as described above enables many advancedfunctionalities for constructing parts using three dimensional printingmethods. Also, the ability to selectively deposit these materialscontinuously also results in a significantly faster deposition process.It should be understood that while two specific resin materials and acore material have been described above, any appropriate resin and corematerial might be used and any number of different resins and coresmight be provided. For example, a single core and a single resin mightbe used or a plurality of cores and a plurality of resins might beprovided in the multi-element printer head.

In a related embodiment, the multi-element printer head 1500 includes anair nozzle 1508 which enables pre-heating of the print area and/or rapidcooling of the extruded material, see FIG. 33. The inclusion of the airnozzle 1508 enables the formation of structures such as flying leads,gap bridging, and other similar features. For example, a conductive corematerial may be extruded by the multi-element printer head 1500 with aco-extruded insulating plastic, to form a trace in the printed part. Theend of the trace may then be terminated as a flying lead. To achievethis, the multi-element printer head would lift, while commensuratelyextruding the conductive core and insulating jacket. The multi-elementprinter head may also optionally cool the insulating jacket with the airnozzle 1508. The end of the wire could then be printed as a “strippedwire” where the conductive core is extruded without the insulatingjacket. The cutting mechanism 8 may then terminate the conductive core.Formation of a flying lead in the above-noted manner may be used toeliminate a stripping step down stream during assembly.

The above embodiments have been directed to three dimensional printersthat print successive filaments of continuous core reinforced filamentin addition to pure resins and their core materials to create a threedimensional part. The position of continuous cores or fibers can also beused with three dimensional printing methods such as stereolithographyand selective laser sintering to provide three dimensional parts withcore reinforcements provided in selected locations and directions asdescribed in more detail below.

For the sake of clarity, the embodiment described below is directed to astereolithography process. However, it should be understood that theconcept of depositing a continuous core or fiber prior to or duringlayer formation can be applied to any number of different additivemanufacturing processes where a matrix in liquid or powder form tomanufacture a composite material including a matrix solidified aroundthe core materials. For example, the methods described below can also beapplied to Selective Laser Sintering which is directly analogous tostereolithography but uses a powdered resin for the construction mediumas compared to a liquid resin. Further, any of the continuous corefilaments noted above with regards to the continuous core reinforcedfilaments may be used. Therefore, the continuous cores might be used forstructural, electrical conductivity, optical conductivity, and/orfluidic conductivity properties.

In one embodiment, a stereolithography process is used to form a threedimensional part. In stereolithography, the layer to be printed istypically covered with resin that can be cured with UV light, a laser ofa specified wavelength, or other similar methods. Regardless of thespecific curing method, the light used to cure the resin sweeps over thesurface of the part to selectively harden the resin and bond it to theprevious underlying layer. This process is repeated for multiple layersuntil a three dimensional part is built up. However, in typicalstereolithography processes, directionally oriented reinforcingmaterials are not used which leads to final parts with lower overallstrength.

In order to provide increased strength as well as the functionalitiesassociated with different types of continuous core filaments includingboth solid and multifilament materials, the stereolithography processassociated with the deposition of each layer can be modified into atwo-step process that enables construction of composite componentsincluding continuous core filaments in desired locations and directions.More specifically, a continuous core or fiber may be deposited in adesired location and direction within a layer to be printed. Thedeposited continuous core filament may either be completely submerged inthe resin, or it may be partially submerged in the resin. After thecontinuous fiber is deposited in the desired location and direction, theadjoining resin is cured to harden around the fiber. This may either bedone as the continuous fiber is deposited, or it may be done after thecontinuous fiber has been deposited as the current disclosure is notlimited in this fashion. In one embodiment, the entire layer is printedwith a single continuous fiber without the need to cut the continuousfiber. In other embodiments, reinforcing fibers may be provided indifferent sections of the printed layer with different orientations. Inorder to facilitate depositing the continuous fiber in multiplelocations and directions, the continuous fiber may be terminated using asimple cutting mechanism, or other appropriate mechanism, similar tothat described above. In some applications, the same laser that is usedto harden the resin may be used to cut the continuous core filament.

FIG. 34 depicts an embodiment of the stereolithography process describedabove. As depicted in the figure, a part 1600 is being built on a platen1602 using stereolithography. The part 1600 is immersed in a liquidresin material 1604 contained in a tray 1606. The liquid resin materialmay be any appropriate photopolymer. In addition to the resin bath,during formation of the part 1600, the platen 1602 is moved tosequentially lower positions corresponding to the thickness of a layerafter the formation of each layer to keep the part 1600 submerged in theliquid resin material 1604. During the formation of each layer, acontinuous core filament 1608 is fed through a nozzle 1610 and depositedonto the part 1600. The nozzle 1610 is controlled to deposit thecontinuous core filament 1608 in a desired location as well as a desireddirection within the layer being formed. Additionally, in someembodiments, the feed rate of the continuous core filament 1608 is equalto the speed of the nozzle 1610 to avoid disturbing the alreadydeposited continuous core filaments. In the depicted embodiment, as thecontinuous core filament 1608 is deposited, a laser 1612, or otherappropriate type of electromagnetic radiation, is directed to cure theresin surrounding the continuous core filament 1608 in a location 1614behind the path of travel of the nozzle 1610. The distance between thelocation 1614 and the nozzle 1610 may be selected to allow thecontinuous core filament to be completely submerged within the liquidresin prior to curing as well as to avoid possible interference issuesby directing the laser 1612 at a location to close to the nozzle 1606.The laser is generated by a source 1616 and is directed by acontrollable mirror 1618. The three dimensional printer also includes acutting mechanism 1620 to enable the termination of the continuous corefilament as noted above.

In another embodiment of a stereolithography process, the depositedcontinuous core filament is held in place by one or more “tacks”. Thesetacks correspond to a sufficient amount of hardened resin material thatholds the continuous core filament in position while additional corematerial is deposited. The balance of the material can then be curedsuch that the cross linking between adjacent strands is maximized. Anynumber of different hardening patterns might be used to providedesirable properties in the final part. For example, when a sufficientnumber of strands has been deposited onto a layer and tacked in place,the resin may be cured in beads that are perpendicular to the directionof the deposited strands of continuous core filament. Without wishing tobe bound by theory, curing the resin in a direction perpendicular to thedeposited strands may provide increased bonding between adjacent strandsto improve the part strength in a direction perpendicular to thedirection of the deposited strands of continuous core filament. While aparticular curing pattern is described, other curing patterns are alsopossible as would be required for a desired geometry and directionalstrength.

FIG. 35 depicts one embodiment of the stereolithography processdescribed above. As depicted in the figure, the continuous core filament1608 is tacked in place at multiple discrete points 1622 by the laser1612 as the continuous core filament is deposited by a nozzle, notdepicted. After depositing a portion, or all, of the continuous corefilament 1608, the laser 1612 is directed along a predetermined patternto cure the liquid resin material 1604 and form the current layer.Similar to the above system, the laser, or other appropriateelectromagnetic radiation, is generated by a source 1616 and directed bya controllable mirror 1618. As illustrated by the figure, the liquidresin material 1604 may be cured in a pattern corresponding to lines1624 oriented perpendicular to the direction of the deposited strands ofcontinuous core filament 1608. Without wishing to be bound by theory,since the cure front is perpendicular to the strands of continuous corefilament 1608, the crosslinking between the strands is increased. Itshould be understood, that if separate portions of the layer includestrands of continuous core filament oriented in different directions,the cure pattern may include lines that are perpendicular to thedirection of the strands of continuous fibers core material in eachportion of the layer. While a particular cure pattern with lines thatare oriented perpendicular to the continuous fibers are described, otherpatterns are also possible including cure patterns of lines that areoriented parallel to the continuous fibers as the current disclosure isnot limited to any particular orientation of the cure pattern.

Similar to the three dimensional printing processes described above withregards to depositing a continuous core reinforced filament, it may bedesirable to avoid the formation of voids along the interface betweenthe continuous core filament and the resin matrix during thestereolithography process in order to form a stronger final part.Consequently, it may be desirable to facilitate wetting of thecontinuous core filament prior to curing the liquid resin material. Insome embodiments, wetting of the continuous fiber may simply require aset amount of time. In such an embodiment, the liquid resin material maybe cured after a sufficient amount of time has passed and may correspondto a following distance of the laser behind the nozzle. In otherembodiments, the continuous core filament may be a continuousmultifilament core material. Such embodiment, it is desirable tofacilitate wicking of the liquid resin material between the multiplefilaments. Wetting of the continuous fiber and wicking of the resinbetween the into the cross-section of the continuous multifilament coremay be facilitated by maintaining the liquid resin material at anelevated temperature, using a wetting agent on the continuous fiber,applying a vacuum to the system, or any other appropriate method.

Having described several systems and methods for forming parts usingthree dimensional printing processes, as well as the materials used withthese systems and methods, several specific applications and componentsare described in more detail below.

In the simplest application, the currently described three dimensionalprinting processes may be used to form parts using composite materialswith increased structural properties in desired directions and locationsas described above. In another embodiment, optically or electricallyconductive continuous cores may be used to construct a part withinductors, capacitors, antennae, transformers, heat syncs, VIA's,thermal VIA's, and a plurality of other possible electrical and opticalcomponents formed directly in the part. Parts may also be constructedwith fluid conducting cores to form fluid channels and heat exchangersas well as other applicable fluidic devices and components.

In some embodiments, a part may also be constructed with sensors, suchas strain gauges, formed directly in the part to enable structuraltesting and structural health monitoring. For example, a cluster ofprinted copper core material can be added to a layer to forming a straingauge. Similarly, an optical fiber can be selectively added to the partfor structural monitoring reasons. Optical fibers can also be printed ina loop to form the coil of a fiber optic gyroscope with a plurality ofpossible advantages including longer loop lengths for increasedsensitivity as well as component integration and simplifiedmanufacturing. For example, the optical coil of the gyro can be printedinside of the associated external container, as part of a wing, orintegrated with any number of other parts. Additionally, an opticalfiber could be printed as part of a shaft encoder for an electricalmotor, which could also be formed using three dimensional printing.

FIG. 36 illustrates a printed part incorporating many of the componentsdescribed above that are formed directly in the part using the describedthree dimensional printing processes. The printed part 1700 includesprinted electrical traces 1702 for connecting the printed electricalcomponents as well as a printed inductor 1704 and a printed antennae1706 connected by the printed electrical traces 1702. The printed part1700 also includes a printed fiber optic cable 1708. Additionally,depending on the embodiment, the printed part 1700 may include contactsor leads, not depicted, for connecting other components such as chip1710 and connectors 1712 to the printed part.

FIGS. 37-39 depict the printing and formation process for a multilayerprinted circuit board (PCB) using additive manufacturing. As insubtractive PCB layout, a pattern of pads and traces can be designed,and then printed, as illustrated in the figures. However, the process ofadditive manufacturing of a PCB is simple enough to perform on a benchusing one machine, thereby enabling a substantial acceleration of thedesign cycle.

FIG. 37 depicts printing of a multi-layer PCB 1800, on a build platen16. The PCB 1800 is formed with a conductive core material 1802 and aninsulating material 1804 which are deposited using a printer headincluding a heated extrusion nozzle 10 and cutting mechanism 8. Similarto the multi element printer head described above, the conductive corematerial 1802 and insulating material 1804 may be selectively depositedeither individually or together. Further, in some embodiments theconductive core material 1802 is solid to minimize the formation ofvoids in the deposited composite material. When the conductive corematerial 1802 is printed without the insulating material 1804 a void1806 can be formed to enable the subsequent formation of vias for use inconnecting multiple layers within the PCB 1800. Depending on the desiredapplication, the void 1806 may or may not be associated with one or moretraces made from the conductive core material 1802.

FIGS. 38 and 39 depict several representative ways in which thecurrently described three dimensional printer could be used to formvarious structures in a printed circuit board 1800. As above, theprinted circuit board 1800 can be printed with various combinations oftraces and voids. For example, voids 1812 are associated with a singlepiece of the conductive core material 1802 which acts as a trace. Thevoids 1812 are subsequently filled with solder or solder paste to formsolder pads 1814. In a similar fashion, the void 1816 is associated withtwo traces and can also be filled with solder or solder paste to form anelectrically connected via 1818 between two or more printed layers. Asan alternative to the above, a void 1820 may not be associated with atrace. Such a void may also be filled with solder or solder paste tofunction as a thermal via 1822. While the solder and/or solder paste maybe applied separately, in one embodiment, the solder fill can be doneusing an optional print head 1810 which is used to dispense solder or anequivalent electrical binding agent 1808. The solder may be applied as amolten solder, or as a solder paste for post processing thermal curingusing any appropriate technique. The ability to print various componentsand traces within a circuit board coupled with the ability to applysolder and/or solder paste, may help to further accelerate theprototyping process of a printed circuit board. In addition to theabove, separate components may be placed on the printed circuit board bythe same machine, another machine, or manually. Subsequently, theprinted circuit board can be heated to bond the separate components tothe printed circuit board and finish the part. It should be understoodthat while manufacturing processes for a printed circuit board describedabove, the ability to selectively form various structures within a threedimensional printed component can be used for any number of differentapplications.

The presently described three dimensional printing systems and methodsmay also be used to form composite structures. A schematicrepresentation of a composite structure is depicted in FIG. 41A whichshows a sandwich panel composite part. The top section 1900, and bottomsection 1902, are printed using a continuous core reinforced filament toform relatively solid portions. In contrast, the middle section 1904 maybe printed such that it has different properties than the top section1900 and the bottom section 1902. For example the middle section 1904may include multiple layers printed in a honeycomb pattern using acontinuous core reinforced filament, a pure resin, or even a threedimensionally printed foaming material. This enables the production of acomposite part including a lower density core using a three dimensionalprinter. Other composite structures that are not easily manufacturedusing typical three dimensional printing processes may also bemanufactured using the currently described systems, materials, andmethods.

While several different types of applications are described above, itshould be understood that the three dimensional printing systems andmaterials described herein may be used to manufacture any number ofdifferent structures and/or components. For example, thethree-dimensional printing systems and materials described herein may beused to manufacture airplane components, car parts, sports equipment,consumer electronics, medical devices, and any other appropriatecomponent or structure as the disclosure is not limited in this fashion

In addition to using the continuous core reinforced filaments to formvarious composite structures with properties in desired directions usingthe fiber orientation, in some embodiments it is desirable to provideadditional strength in directions other than the fiber direction. Forexample, the continuous core reinforced filaments might includeadditional composite materials to enhance the overall strength of thematerial or a strength of the material in a direction other than thedirection of the fiber core. For example, FIG. 41B shows a scanningelectron microscope image of a carbon fiber core material 2000 thatincludes substantially perpendicularly loaded carbon nanotubes 2002.Without wishing to be bound by theory, loading substantiallyperpendicular small fiber members on the core increases the shearstrength of the composite, and advantageously increases the strength ofthe resulting part in a direction substantially perpendicular to thefiber direction. Such an embodiment may help to reduce the propensity ofa part to delaminate along a given layer.

In traditional composites, fibers are laid up, then a hole is drilledafter the fact (subtractive machining). This is illustrated in FIG. 40Awhich illustrates multiple layers 1850, which may either be formed usingpure polymer filaments or core reinforced filaments. As also depicted inthe figure, a hole 1852 is subsequently formed in the part using adrilling or other appropriate machining process. In contrast, in someembodiments, a core reinforced filament 1854 is used to form a holedirectly in a part, see FIGS. 40B and 40C. More specifically, the corereinforced filament 1854 comes up to the hole, runs around it, thenexits from the direction it came, though embodiments in which thefilament exits in another direction are also contemplated. A benefitassociated with this formation method is that the hole is reinforced inthe hoop direction by the core in the core reinforced filament. Asillustrated in FIG. 40B, the core reinforced filament 1854 enters thecircular pattern tangentially. This is good for screws that will betorqued in. In another version, the core reinforced filament 1854 enterthe circular pattern at the center of the circle. Of course, it shouldbe understood that other points of entering the pattern are alsopossible. In one embodiment, the entrance angle is staggered in eachsuccessive layer (also described in a PPA). For example, if there aretwo layers, the entering angle of the first layer may be at 0 degreeswhile the entering angle for the second layer may be at 180 degrees.This prevents the buildup of a seam in the part. If there are 10 layers,the entering angle may be every 36 degrees or any other desired patternor arrangement.

As noted above, typical towpregs include voids, this may be due toconsiderations such as at a temperature and rate at which a greentowpregs pass through a nozzle as well as the difference in areas of thegreen and impregnated towpregs. Due to the relatively high-viscosity ofthermoplastics, for example, sections of the extruded material alsotypically are not fully wetted out. These “dry” weak points may lead topremature, and often catastrophic, component failure.

In view of the above, it is desirable to improve the wetting orimpregnating of towpregs during the impregnation step. One way in whichto do this is to pass a material including a core of one or more fibersand a matrix material through a circuitous path involving multiplechanges in direction of the material while the matrix material ismaintained in a softened or fluid state. For example, in the case of apolymer matrix, the polymer may be maintained at an appropriatetemperature to act as a polymer melt while the circuitous path functionsto mechanically work the matrix material into the fibers. This processmay help to reduce the processing time while enhancing the fiber wet-outto provide a substantially void free material. Moreover, reducing theresidence time of the matrix material, such as a thermoplastic matrixmaterial, at high temperature reduces degradation of the material whichresults in further strengthening of a resultant part formed using thecomposite material. The above noted process may be used for bothcontinuous, and semi-continuous, core materials.

In some embodiments, a circuitous path used to form a desired materialis part of a standalone system used to manufacture a consumablematerial. Alternatively, in other embodiments, a circuitous path isintegrated in the compression stage of a print head. In such anembodiment, friction within the print head may be minimized by using oneor more smooth walled guide tube with a polished surface. Further, theone or more guide tubes may be close-fitting relative to the material,such that the compressed fiber does not buckle and jam the print head.

FIG. 42 depicts one possible embodiment of a three-dimensional printerhead 2102 including a circuitous path impregnation system. In thedepicted embodiment, a continuous core filament 2100 is driven by a feedmechanism 2110 (e.g. the depicted rollers), into a cutting mechanism2104, through a receiving section 2106, and into a heated zone 2112 ofthe nozzle. When passing through the heated zone 2112, the continuouscore filament 2100 passes through a circuitous path 2108 correspondingto a channel that undergoes at least a first bend in a first directionand a second bend in a second direction prior to the material beingextruded from the nozzle into one or more layers 2116 on a print bed2118. The resulting shape of the circuitous path forms a somewhatsinusoidal path. However, it should be understood that any number ofbends and any desired curvature might be used to form the circuitouspath. Similar to the above noted printer heads, the printing process maybe controlled using a controller 2114 which may also control theimpregnation processes. The advantages associated with the depictedembodiment is provided by the back and forth mechanical motion of thecontinuous core filament 2100 within the circuitous path 4 which aids inthe impregnation of the input material.

FIG. 43A illustrates one possible embodiment of the continuous corefilament 2100 when it is input to the system. As illustrated in thefigure, the continuous core filament 2100 corresponds to a commingledgreen towpreg including one or more fibers 2120 bundled with a matrixmaterial 2122 in the form of fibers or particles. After passing throughthe heated zone and the circuitous path, the continuous core filament2100 has been fully wetted by the matrix material 2122 to provide asubstantially void free continuous core filament, see FIG. 43B.

In another embodiment, the circuitous path is provided by offset rollerswhich may either be stationary, or they may be constructed toadvantageously open during initial threading to provide a straightthrough path and subsequently close to provide the desired circuitouspath. FIGS. 44A and 44B show one possible implementation of such anembodiment. As depicted in the figures, three or more rollers 204 areplaced within the printer head 2102 to provide the desired circuitouspath. During use, the continuous core filament 2100 is fed through theoffset rollers by the feeding mechanism 2110 and through the printerhead. FIG. 44B depicts an optional loading strategy. In such anembodiment, the rollers 2124 are selectively movable between a firstposition in which they form a circuitous path as illustrated in FIG. 44Aand a second position in which they do not obstruct a path between aninlet and outlet of the printer head 2102 in order to facilitatethreading of the system with the continuous core filament 2100, see FIG.44B. After the material has threaded past the rollers 2124, they mayreturn to the first position to form the circuitous path depicted inFIG. 44A.

In another embodiment, not depicted, a circuitous path located within aprint head is formed by a flexible tube such as apolytetrafluoroethylene tube. The flexible tube is selectively placed ina straight configuration to permit threading of the printer head.Subsequently, the flexible tube is deformed into a circuitous path afterthreading has been completed to facilitate impregnation of a continuouscore filament passing there through as described above.

In some instances, it is desirable to provide a fully wetted orimpregnated material to the feeding mechanism of a printer head. In suchan embodiment, a circuitous path wet-out of a continuous core filament2100 is performed as a pre-treatment step within the tension side of athree-dimensional printer, prior to feeding the resulting substantiallyvoid material into the compressive side of the three-dimensionalprinter, see FIG. 45. As depicted in the figure the continuous corefilament 2100 enters a pre-conditioner 2124. As noted above, whenentering the pre-conditioner 124, the continuous core filament 2100 maycorrespond to a comingled towpreg including one or more fibers andmatrix material. As the continuous core filament 2100 passes through thepre-conditioner 2124, it is heated and passes through a circuitous pathwhich may be provided by a set of offset rollers 2126, or otherappropriate configuration to facilitate impregnation of the material.After passing through the pre-conditioner 2124, the continuous corefilament 2100 passes through the feeding mechanism 2110 corresponding toa set of drive rollers. The feeding mechanism 2110 feeds the continuouscore filament 2100 into a print head 2130 including a vacuum pressuresystem 2132. The vacuum pressure system 2132, or other appropriatesystem, varies a pressure applied to the continuous core filament 2100within the print head. Without wishing to be bound by theory, thesepressure variations may facilitate impregnation of the fibers and burstair pockets within the towpreg. In another preferred embodiment, acontinuous vacuum line is used for the vacuum pressure system 2032instead of the oscillating pump as depicted in the figure. Additionally,while a vacuum may be applied to vary a pressure within the print head,embodiments in which positive pressures are applied to the print headare also contemplated.

In yet another embodiment, the matrix material contained within a greencontinuous core filament is worked into the fibers by passing throughone or more compressive roller sets while the matrix is hot and capableof flowing. FIG. 46 shows one embodiment of a three-dimensional printhead 2034 including a first and second set of compression rollers 2136disposed within the print head. As depicted in the figure, thecontinuous core filament 2100 passes through the print head where it isheated and subjected to two subsequent compressions from the two sets ofcompression rollers. While two sets of rollers are depicted in thefigures, additional rollers within the print head may also be used.

In another embodiment, oscillating pressures and/or vacuums a reused towork the matrix material into the fiber core of a continuous corefilament. Without wishing to be bound by theory, applying reducedpressures, or increased vacuums, to the material removes voids.Conversely, applying increased pressures, or decreased vacuums, thenforces the resin deeper into the fiber towpreg as the air pressurearound said towpreg increases. The above noted process may either beperformed completely with vacuums, positive pressures, or a combinationof the two as the disclosure is not so limited. For example, a materialmight be cycled between ambient pressure and a high pressure, betweenambient pressure and a vacuum, or between positive pressures andvacuums.

In the above embodiments, mechanically working the matrix into the fibercores enables the production of substantially void free towpregs from avariety of starting materials. For example, comingled towpregs can beused. In an additional embodiment, a flat towpreg in which the polymermatrix is only partially wicked into the underlying fibers is subjectedto the circuitous path wetting method described above to wet out thetowpreg. In addition to enabling the manufacture of various types oftowpregs, if used as a pre-treatment, a precision extrusion die can beused to form the impregnated material into a desired size and shape forextrusion from a three dimensional printer. For example, the materialmay have a circular cross section though any other appropriately shapedcross section might also be used.

When desirable, a precision roller set can be used to maintain aconstant thickness along a relatively wider width of material outputfrom a print head 2102. Such an embodiment may be of use when dealingwith wider materials such as flat towpregs. FIG. 47 shows a print head2102 translating in a first direction. A nozzle 2136 of the print headis attached to a trailing compression roller 2138. The roller imparts acompressive force to the material deposited on to the onto print bed2140. Depending on the embodiment, the trailing roller 2138 canarticulate around the Z axis using any number of different mechanisms.For example, in one embodiment, the print head 2102 is free-rotating ona bearing, such that the roller always trails the direction of travel ofthe print head. In another embodiment, the entire print head 402 isconstructed to rotate. Alternatively, the print bed 2140 may be rotatedto achieve the desired trailing and displacement.

FIG. 48 shows one embodiment of a high-speed continuous core printercapable of using the above described materials. In the depictedembodiment, the printer includes a print arm 2200 including a pluralityof nozzles. The nozzles include a pure resin nozzle 2202 adapted toprint pure resin 2208. The print arm 2200 also includes a continuouscore filament nozzle 2204 adapted to print a continuous core filament2210 for use in fine detail work. Additionally, the print arm 2200includes a tape dispensing head 2206 capable of printing one or moreprintable tapes 2212. The tape dispensing head enables large infillsections to be printed quickly using the noted printable tapes. However,fine detail work and gaps that cannot be filled in by the tape can befilled by either the pure resin nozzle 2202 or continuous core filamentnozzle 2204 as the disclosure is not so limited. The above noted methodand system using wide tape fills greatly improves the speed of aprinter, enabling higher throughput, and commensurately lower cost.

As noted above, in some embodiments, it is desirable to provide amaterial with a smooth outer surface for a variety of reasons. Asdetailed below, the smooth outer surface, a desired shape, and/or adesired size may be obtained in a variety of ways.

In one embodiment, a core reinforced filament includes an internalportion including axially aligned continuous or semi-continuous fibers,or other materials, in the form of a tow, bundle, yarn, string, rope,thread, twine, or other appropriate form. The internal portion alsoincludes a matrix in which the fibers are embedded. The core reinforcedfilament also includes an external coating disposed on the internalportion of the filament. The external coating may be shaped and sized toprovide a desired cross-sectional shape and size. The resulting corereinforced filament may be used in a three dimensional printing processas described herein as well as other appropriate three dimensionalprinting processes as the disclosure is not so limited.

In a related embodiment, a method for manufacturing a core reinforcedfilament includes embedding a tow, bundle, yarn, string, rope, thread,cord or twine in a polymer matrix using any appropriate method. Theresulting filament is subsequently extruded with a polymer to form theexternal coating noted above. As described in more detail below, theexternal coating may be made from the same material, or a differentmaterial, as the matrix material of the internal portion of thefilament.

FIG. 49A depicts a process to make a fully-wetted or impregnated corereinforced filament with a smooth outer coating for use in athree-dimensional printing system. As depicted in the figure, acontinuous core element 2300 is pulled into a co-extrusion die 2302. Insome embodiments, the continuous core element 2300 is subjected tovarious pretreatments at 2301 prior to entering the co-extrusion die2302 as described in more detail below. Once introduced into theco-extrusion die 2302 the continuous core element 2300 is impregnatedwith matrix material 2306 at a mixing point 2304. Either during, orprior to wetting or impregnation of the continuous core element with thepolymer, an optional vacuum step may be employed to remove entrapped airfrom the continuous core filament. FIGS. 49B and 49C depict crosssectional views of various starting continuous core elements 2300 whichmay be towpregs including a plurality of aligned reinforcing fibers. Ascomplete wetting or impregnating is the primary goal of this step (asopposed to merely coating in traditional co-extrusion dies), thetemperature and pressure of the mixing step may be increased to achievethe desired full-wetting/impregnating through the fiber bundle.Alternatively, or in addition to the above, a circuitous path and/orvarying pressure may be applied as described above to further facilitatewetting/impregnation of the material.

As many carbon fiber and fiberglass towpregs are initially in atape-like format, the die exit 2308 of the co-extrusion die may act toconsolidate the continuous core element and polymer matrix material intoa desired shape and size to provide a smooth, constant diameter,composite filament. However, the filament will start to distortdown-stream of the coextrusion die as occurs with typical filamentmanufacturing processes. The inventors have recognized that thisdistortion is an artifact of cooling the extrusion without support whichis somewhat akin to ejecting an injection molded part too soon whichthen warps when outside of the mold. Consequently, in some embodiments,a cooling tube 2312 and operatively coupled cooling element 2310, suchas a cooling jacket, are aligned with and support the extruded material.Consequently, the extruded core reinforced filament is permitted to coolwhile being constrained to a desired size and shape. Lubricating agentsmay advantageously be applied to the filament upon entry to the tube, orat points along a length of the tube. The lubricating agents may eitherevaporate, or be washed off at the later time. The lubricants mayfunction to reduce the dragging friction of the core reinforced filamentwithin the tube to substantially prevent, or at least reduce, “skipping”or surface roughness from dragging the filament through the cooling tubeduring cooling. Depending on the core material, and its correspondingcompressibility and ductility, the cooling tube may be built with aseries of different inner diameter “dies” to achieve a desired shape andsize. Alternatively, a plurality of discrete “cooling dies” might beused in place of a cooling tube for certain materials. An output corereinforced material 2314 may exhibit cross sections similar to thosedepicted in FIGS. 49E-49F. Depending on the amount of compression usedin the cooling tube, or die, the material may exhibit varying crosssectional profiles that conform either more or less to a shape of thetube or die.

In some embodiments, the core reinforced filament is fed into a secondco-extrusion die 2316 where it is coated with another matrix material2318, such as a polymer or resin, prior to being output through the dieexit 2320 as a coated core reinforced filament 2322. This outer coating2326 is disposed on the internal portion 2324. The outer coating 2326may be made from the same material, or a different material, as thematrix material 2306 in the internal portion. Therefore, the outercoating 2326 may be selected to provide a desired performancecharacteristics such as bonding to previously deposited layers, wearresistance, or any other number of desired properties. Additionally, insome embodiments, the outer coating 2326 provides a smooth, fiber-freeouter diameter as shown in the cross-section is presented in FIGS.49G-49I. FIG. 49G presents an embodiment of the core reinforced filamentincluding an internal portion 2324 and an outer coating 2326 formed withdifferent matrix materials as well as a plurality of filaments formingthe continuous core. FIG. 49H depicts an embodiment of the corereinforced filament including an internal portion 2324 and an outercoating 2326 formed with the same matrix material as well as a pluralityof filaments forming the continuous core. FIG. 49I presents anembodiment of the core reinforced filament including an internal portion2324 including a solid continuous core 2300. The inner and outer matrixmaterials may be any appropriate binder used in composites, including,but not limited to, thermoplastics, thermosets, resins, epoxies,ceramics, metals, waxes, and the like.

FIG. 50A depicts an alternative roller-based method to achievefull-wetting/impregnation of the fiber, combined with an outer coating.Similar to the above, the core material 2300 may have a cross-sectionsas depicted in FIGS. 50B and 50C. Additionally, the core material 2300may be subjected to an optional pre-treatment step at 2301. The corematerial 2300 is passed through a set of dispersion rollers 2330 whichare constructed and arranged to flatten the cross-section of the corematerial to a flattened cross-sectional shape 2332 illustrated in FIG.50D. Without wishing to be bound by theory, dispersing the individualfibers of the continuous core into a flattened shape may help tofacilitate wetting/impregnation of the matrix material 2306 when it isintroduced to the flattened continuous core element 2332 at the mixingpoint 2304. Similar to the above, the continuous core element and matrixmaterial may be subjected to a circuitous path and/or varying pressuresto further facilitate impregnation of the matrix material. Additionally,in the depicted embodiment, the system may optionally include a set ofrollers 2334 located downstream from the mixing point 2304. The rollers2334 may apply a force to the composite filament to further force thematrix material 2306 into the continuous core element 2300. Across-section of the resulting composite flattened tape 2336 isillustrated in FIG. 50E. The resultant flattened composite tape 2336 issubsequently fed into a forming die 2338. This step can either beachieved with a heated forming die, that is heated to a sufficienttemperature in order to reflow the material, or the forming die 2338 islocated sufficiently close to the exit of the rollers 2334 such that thecomposite flattened tape is at a sufficient temperature to be formedwhen entering the die. Again, similar to the above, an optional coolingtube 2312 and an associated cooling element 2310 may be associated withthe forming die 2338 in order to support a cross-section of the corereinforced filament 2314 as it cools, see FIGS. 50F-50G. An outercoating may then be applied to the court reinforced filament to forminga coated core reinforced filament 2322 as described above.

While the above described embodiments have been directed to the use of afully wetted, fully wicked material, that is substantially void free, itshould be noted that described outer coatings and impregnation methodsmay be used with materials including voids as well. Additionally, greenmaterials that have not been wetted might also be used with the threedimensional printers described herein. Further, while various shapessuch as flattened tapes and rounded cross-sectional profiles aredescribed above with regards to the manufacturing processes, anyappropriate shape of the material and/or resulting core reinforcedfilament is possible as the disclosure is not so limited.

The composition of the aforementioned two polymer matrix binders used inthe internal portion and outer coating of a composite filament maydiffer by one or more of the following factors: polymer molecularweight, polymer weight distribution, degree of branching, chemicalstructure of the polymer chain and polymer processing additives, such asplasticizers, melt viscosity modifiers, UV stabilizers, thermalstabilizers, optical brighteners, colorants, pigments or fillers.Manufacturing of core reinforced filaments with two different bindercompositions may be practiced in several different ways depending onwhich particular processing characteristic or the property of thefinished part one desires to modify or control.

In one embodiment, it is desirable to preserve the uniform distributionof the fibers in the interior portion of the filament and the circularcross section shape. In such an embodiment, the polymer matrix of theinterior portion may exhibit a higher melting point than the meltingpoint of the polymer matrix in the outer coating. Consequently, theinterior portion of the filament remains in a solid, or at least asemi-solid highly viscous state, when the external coating is applied.Correspondingly, the fibers contained within the continuous core willstay in place and the filament will retain its circular cross-sectionalshape during application of the outer coating polymer matrix byco-extrusion while avoiding migration of the continuous fibers throughthe molten matrix of the interior portion of the filament to the outercoating of the filament during the co-extrusion step.

In another embodiment, it is desirable to improve impregnation/wettingof the fiber towpreg by the matrix binder. Consequently, in someembodiments, a less viscous polymer melt is used as the matrix materialin the interior portion of the filament. Preferably, the polymer matrixmaterial used for the interior portion of the filament should have notonly low viscosity, but also exhibit improved interfacial wetting of thefiber surface. Without wishing to be bound by theory, this may beobtained by matching the surface energy of the imbibing polymer meltwith the surface energy of the continuous fiber material. The polymermatrix material used for the external coating may comprise a polymerwith a higher melt viscosity than the interior matrix polymer. Theexterior polymer matrix material may also exhibit a lower melting pointthan the interior polymer. The wetting properties of the outer coatingmatrix towards the continuous core is of lesser importance as the twoshould not in principle be in direct contact.

In yet another embodiment, is desirable to facilitate the adhesion of anexternal coating to the underlying bundle through the modification ofthe surface energy of the polymer melt and the continuous corefilaments. The surface energy can be controlled by a number of methods,including, but not limited to, varying the content and the type of thepolar groups in the polymer backbone, the addition of surface activecomponents to the melt, for example, surfactants, oils, inorganicfillers etc., exposing the fibers to electric gas discharge plasmas,chemical vapor deposition, ozone, or reactions with, or coating of,surface modifying compounds from solutions.

In another embodiment, surface energy modifiers may also be used tostrengthen the interlayer bonding of the filament as it is deposited bya three dimensional printer. For example, ozone may be deposited by theprint head to promote adhesion of a new layer to an existing layer. Inanother embodiment, the build chamber may be filled with a sufficientproportion of ozone to activate the exposed surfaces.

In yet another embodiment of the present invention, it may beadvantageous to improve the bond strength of freshly extruded fiber-richfilament to the underlying layer by selectively applying a stream ofheated vapor to a small area adjacent to, and/or just ahead of, thedeposition point of the freshly deposited filament.

In another embodiment, it is contemplated that the bond strength betweenthe freshly extruded fiber-rich filament and the underlying layer may beimproved by selectively directing a stream of air or another gasconsisting of a sufficient concentration of ozone toward a small areaadjacent to, and just ahead of, the deposition point of the freshlydeposited filament surface. Ozone readily reacts with the atomicallythick surface layers of organic polymers to create a multitude of polarreactive surface groups, such as hydroxyl, ozonide, peroxide,hydroperoxide, aldehyde and carboxylic groups, which by their veryreactive chemical and/or polar nature facilitate bonding of the surfacelayer to another material, such as ink, adhesive or another polymerbinder.

In yet another embodiment, it is desirable to increase the bondingstrength with a build platform to help prevent lifting off of a part, orsection of a part, from the build platform. Consequently, in someembodiments, a surface energy modifier is applied to the build platformto facilitate the adhesion of the extruded filament to said platform. Insome embodiments, the noted adhesion modification is used to increasethe adhesion of the first bonding layer to the build platform in a fewkey areas, such as the corners of a box, thereby causing greateradhesion where the part is most likely to peel up from the platform. Thecenter of the box, however, may be substantially free of surface energymodifiers to facilitate easy removal.

With regards to the above noted embodiments, it should be understoodthat the timing and/or quantity of deposited ozone, vapor, or othersurface energy modifier may be varied to obtain a desired level ofadhesion.

In another embodiment, a magnetic filler is loaded into the matrixmaterial. The magnetic filler may either be magnetically active, likeiron or steel, or it may be magnetized as the disclosure is not solimited. In the case of continuous core printing of electronics, themagnetic filler could be used to form a three dimensionally printedactuation members. Additionally, the magnetic matrix particles could beused to magnetically stick a part to a printing table during printing,and then release at the conclusion of printing. The magnetic materialmay either be integrated into a final part, or it may advantageously beintegrated into a removable support material with similar matrixexhibiting properties similar to the remainder of the material.

In yet another embodiment, the magnetically active filler particlesenable measurement and detection of the material, or support structure,using x-rays or metallic sensors. For example, using a materialincluding metallic powder in the support material, and not the modelmaterial, would enable easy detection of the removal of all the supportmaterial. In another embodiment, the magnetic material is added to apart, or all, of a part, to enable the detection of intricate featuresin x-ray detection, that would otherwise be invisible.

In some embodiments, a continuous core, such as continuous carbonfibers, is combined with a semi-aromatic polyamides and/or asemi-aromatic polyamide blends with linear polyamides which exhibitexcellent wetting and adhesion properties to the noted continuous carbonfibers. Examples of such semi-aromatic polyamides include blends ofsemi-aromatic and linear polyamides from EMS-Grivory, Domat/Ems,Switzerland, such as Grivory HT1, Grivory HT2, Grivory HT3 and othersimilar blends. By combining continuous reinforced fiber towpregs withhigh-temperature melting and fiber wetting polyamides and their blends,parts may be manufactured which are characterized by exceptionalmechanical strength and long-term temperature stability at usetemperatures 120° C. and higher while ensuring extrudability of thecomposite tow, excellent fiber-matrix wettability, complete fibertowpreg permeation with the resin and excellent shear strength at thefiber-matrix interface.

The optional pre-treatments noted above are intended to facilitate fullwetting of the core material, and wicking of the matrix material intothe centers thereof. Various types of pretreatments can includecategories such as mechanical, rheology, and fiber-wetting pretreaments.The particular method(s) employed will depend on the matrix materialchosen, and the core selected.

Appropriate mechanical pretreatments include, spreading the individualfibers of the core into a flattened ribbon-shaped towpreg by mechanicalor pneumatic means before contacting with the resin or melt (i.e. dipcoating). Alternatively, a towpreg may pass through a melt in a chamberthat is periodically evacuated to expand and remove air bubbles trappedbetween the fibers and to force the resin or melt into the interstitialspace between the fibers when the vacuum is released. Additionally,periodic cycles of higher air pressure may improve the effectiveness ofthe process by changing the size of entrapped air bubbles and forcingthe renewal of the air-fiber interface, thus, facilitating bubblemigration. Additionally, a resin or polymer milk may be injected fromone side of a continuous core such that it is injected through thecontinuous core as compared to simply surrounding it during atraditional coextrusion process. Should be understood that othermechanical pretreatments are also possible.

Appropriate rheological pretreatments of a continuous core include theuse of a low viscosity or high melt flow index resins or polymer melts.Additionally, polymers exhibiting low molecular weights and/or linearchains may be used. Polymers exhibiting a sharp melting point transitionwith a large change in viscosity might also be used. Such a transitionis a typical property exhibited by polyamides. Various features such asmultiple port melt injection, angled channels, as well as fluted orspiral-groove extrusion channel surface “morphologies” may be used toinduce higher melt turbulence and non-laminar melt flow which may resultin enhanced impregnation of the matrix material. Melt viscositymodifiers and lubricants used to lower the effective melt viscosity andimprove slip at the fiber surface might also be used.

Appropriate fiber wetting pretreatments may include precluding the fibersurfaces with a very thin layer of the same or similar polymer from adilute polymer solution followed by solvent evaporation to obtain alike-to-like interaction between the melt and the fiber surface. Polymeror resin solutions in neutral and compatible solvents can haveconcentrations from about 0.1 wt.-% to 1 wt.-% or higher. Additionally,one or more surface activation methods may be used to introduce orchange the polarity of the fiber surface and/or to introduce chemicallyreactive surface groups that would affect wetting/impregnation (contactangle) and adhesion (matrix-fiber interfacial shear strength) byphysically or chemically bonding the polymer matrix with the fibersurface. Several examples of suitable surface activation methodsinclude, but are not limited to: atmospheric pressure surface oxidationin air; air enriched in oxygen, nitrogen oxides, or other reactivegases, such as halogenated, sulfur, silicon or other volatile compounds;as well as a high-voltage corona discharges (a method widely used inactivating polyolefin film surfaces for printing). Low-pressure plasmaactivation techniques in air, oxygen, or the other gases enumeratedabove may also be used to introduce reactive chemical surface groupswith a chemical character defined by the process conditions (time,pressure, discharge energy (electrode bias voltage), residence time andthe composition of the reactive gas. The fiber surface may also bechemically activated using: activation methods in gas and liquid phase,such as silanization in the presence of hexamethyldisilizane (HMDS)vapors, especially at elevated temperatures; and solvent-phase surfacemodification using organosilicon or organotitanium adhesion promoters,such as tris(ethoxy)-3-aminopropylsilane, tris(ethoxy) glycidyl silane,tetraalkoxytitanates and the like.

While the present teachings have been described in conjunction withvarious embodiments and examples, it is not intended that the presentteachings be limited to such embodiments or examples. On the contrary,the present teachings encompass various alternatives, modifications, andequivalents, as will be appreciated by those of skill in the art.Accordingly, the foregoing description and drawings are by way ofexample only.

What is claimed is:
 1. A method for manufacturing a part, the methodcomprising steps of: adhering a coated continuous core reinforcedfilament to a surface; and dragging the coated continuous corereinforced filament from a nozzle of a printhead when the printhead ismoved relative to the surface.
 2. The method of claim 1, wherein thecoated continuous core reinforced filament is substantially void free.3. The method of claim 1, wherein a core of the coated continuous corereinforced filament comprises a multifilament core.
 4. The method ofclaim 1, wherein prior to the step of dragging, the coated continuouscore reinforced filament is adhered to a point on the surface.
 5. Themethod of claim 4, wherein the point is an anchor point.
 6. The methodof claim 5, wherein the core of the coated continuous core reinforcedfilament is substantially impregnated with a matrix material.
 7. Themethod of claim 6, wherein the coating surrounding the coated continuouscore reinforced filament is a matrix material.
 8. The method of claim 6,further comprising affixing the dragged coated reinforced filament to anopposing section of a gap, such that the coated continuous corereinforced filament bridges the gap from the anchor point to the affixedpoint.
 9. A method for manufacturing a part, the method comprising stepsof: coextruding a continuous core reinforced filament and a matrixmaterial; adhering the coated continuous core reinforced filament to asurface; and dragging the coated reinforced filament when a printhead ismoved relative to the part.
 10. The method of claim 9, furthercomprising, prior to the step of adhering, coating the continuous corereinforced filament with the matrix material.
 11. The method of claim10, wherein the coating step occurs at a mixing point.
 12. The method ofclaim 9, further comprising extruding a coated continuous corereinforced filament from a nozzle of the printhead.
 13. The method ofclaim 9, wherein the adhering step comprises applying a compactionpressure to the coated continuous core reinforced filament.
 14. Themethod of claim 9, wherein the adhering step comprises compressing thecoated continuous core reinforced filament.
 15. The method of claim 14,wherein compressing the coated continuous core reinforced filamentspreads the plurality of strands of the coated continuous corereinforced filament.
 16. The method of claim 15, wherein compressing thecoated continuous core reinforced filament spreads the coated continuouscore reinforced filament into an adjacent coated continuous corereinforced filament of a same layer and an underlying material of thepart.
 17. The method of claim 13, wherein the compaction pressure isapplied by printhead.
 18. The method of claim 9, wherein the adheringstep further comprises heating to reflow the matrix material.
 19. Themethod of claim 9, wherein the continuous core reinforced filament is atowpreg.
 20. The method of claim 19, wherein the towpreg comprises aplurality of axially aligned reinforcing fibers.
 21. The method of claim9, wherein the continuous core reinforced filament is a prepreg.
 22. Themethod of claim 21, wherein the prepreg comprises multiple continuousstrands preimpregnated with a resin already wicked into the strands. 23.The method of claim 9, wherein the continuous core reinforced filamentis combined with matrix material at a nozzle outlet.
 24. The method ofclaim 9, wherein the matrix material comprises a thermoplastic, athermoset, a resin, or an epoxy.
 25. A method for manufacturing a part,the method comprising steps of: coating an outer surface of at least onecontinuous core reinforced filament with a matrix material at acoextrusion die of a printhead to form a coated continuous corereinforced filament; adhering the at least one coated continuous corereinforced filament to a surface; and dragging the at least one coatedcontinuous core reinforced filament when the printhead is moved relativeto the part.
 26. The method of claim 25, further comprising, prior tothe step of adhering, extruding the coated continuous core reinforcedfilament from a nozzle of the printhead.
 27. The method of claim 25,further comprising a step of impregnating the at least one continuouscore reinforced filament with matrix material such that at least onecontinuous core reinforced filament is wicked.
 28. The method of claim25, wherein the step of coating occurs at a mixing point.
 29. The methodof claim 25, wherein the matrix material comprises a thermoplastic, athermoset, a resin, or an epoxy.
 30. The method of claim 1, furthercomprising, prior to the step of adhering, steps of: impregnating acontinuous core element with a matrix material at a first coextrusiondie of a printhead to form a continuous core reinforced filament;introducing the continuous core reinforced filament within a secondcoextrusion die of the printhead; and coating an outer surface of thecontinuous core reinforced filament at the second coextrusion die of theprinthead to form a coated continuous core reinforced filament.